2 Camera equipment

Despite the proliferation of digital imaging systems, learning about and understanding the characteristics of the different formats in film-based systems is useful and important in the understanding of photography. Furthermore, many digital camera systems have evolved directly from film cameras, particularly in professional photography. Although there are significant differences in methods of working with the two different media, many of the skills and understanding required to use the cameras, to compose and manipulate image shape, perspective, depth of field, image blur, and to correctly expose a subject remain the same. Furthermore, without considering film-based systems, there is no benchmark for evaluating the merits of digital camera systems.

At the time of writing, although smaller formats are now dominated by digital equipment, the limited choice and high cost of digital large format can be prohibitive; therefore, a number of professionals still work with film. This chapter begins by considering how photography has changed with the adoption of digital camera systems, before introducing the main types of film and digital camera designs and image formats. It also considers the different role of the camera in the imaging process. Some of the features which are specific to digital cameras are highlighted, before moving on to descriptions of the properties of the main formats of cameras, particularly those used in professional photography, identifying the differences between film and digital in each category. It attempts to provide an overview, necessary when considering the purchase of camera equipment. It also aims to highlight the way in which camera design influences the method and type of photographic work. Included is a section on specialized accessories. A summary is provided at the end.

The digital revolution

The first patents for devices capturing images electronically were filed as far back as 1973. Kodak created a prototype digital camera in 1975 using a charge-coupled device (CCD), recording black and white images on to digital cassette tape; however, it was built to test the feasibility of digital capture using solid-state sensors, rather than as a camera for manufacture (due to its bulky size and a weight of nearly 3.6 kg). It was not until 1981 that Sony developed a camera using a CCD, suitable to be hand held and available to the consumer. The birth of digital still cameras as we know them today happened in 1988, when Fuji showcased their camera, the DS-1P, at Photokina. Early digital formats could not compete with their film equivalents in terms of cost or quality; digital cameras as a practical option for consumers were not really available until the mid-1990s. Since then the digital market and technologies have grown exponentially.

The move to digital imaging by many photographers has involved a preceding step via ‘hybrid’ imaging – that is, capture on film followed by digitization using a scanner. However, in the last 10 years, huge advances in sensor technology, computing capabilities and the widespread adoption of broadband (ADSL) Internet connection by the consumer have meant that digital imaging has finally arrived. For example, most households in Britain now own at least one computer and the majority of new mobile phones have a built-in digital camera. The digital camera market has therefore been advanced by the consumer market and of course the widespread use of imaging on the Internet.

Immediate results and the ability to easily manipulate, store and transmit images have become a priority in many disciplines, with some sacrifice in the quality that we expect in our images. In the professional market there have also been compromises between versatility of systems and image quality, but progress towards the uptake of entirely digital systems has been somewhat slower. In some types of photography, image quality requirements and the lack of digital equipment available in large format has meant that film-based systems are still common. With the developments in sensor size and resolution and a wider range of medium-format cameras and digital backs, however, many photographic specialisms have now embraced a predominantly digital workflow from capture to output.

Figure 2.1 The main types of film camera design: (a) compact rangefinder camera; (b) a single-lens reflex camera, 35 mm format; (c) a single-lens reflex camera, medium format; (d) a twin-lens reflex, medium-format camera; (e) a view camera.

Camera design

Fundamentally, all cameras consist of the same basic components: a light-tight box, a method of focusing the image on to the image plane, an image sensor to capture and record the image, and some means of controlling exposure. However, the history of camera design has seen many developments, leading to ever more sophisticated and portable devices, culminating in the twentieth century with the addition of electronic components and, of course, the introduction of digital cameras. Traditionally, camera systems using film have been classified by the viewfinder system and the image format, i.e. the size and dimensions of the captured image. Some examples are illustrated in Figure 2.1. In professional photography, three main film formats and corresponding camera systems have dominated: small-format 135 roll film commonly termed ‘35 mm’, which has dimensions of 24 × 36 mm, where the camera designs are mostly single-lens reflex (SLR) systems with interchangeable lenses; medium-format 120 roll film, with a range of sizes (45 × 60 and 60 × 60 mm are common), where cameras are most commonly SLR modular camera systems with a removable film back; and large-format ‘view’ cameras, with the most common film format of 4 × 5 inches (97 × 122 mm) – these are closest to very early camera designs, incorporating a bellows extension between movable lens and film planes.

Today, many (but not all) of the manufacturers previously associated with film-based photography have wound down their production of film cameras to concentrate on the development of digital camera systems. The market has also widened, with the introduction of digital cameras developed by companies not previously involved in photography, but with a history in a related area, such as video or electronics. The consequence of this has been a proliferation of different types of camera design and camera features where previously they could be more or less classified into three or four main types. While the developments have been exciting, the variety can be confusing when trying to decide on what type of camera system to purchase.

Digital camera equipment is less easily classified by image format than film, simply because of the huge variation in sensor size. Cameras can, however, be put into broad categories based upon the market for which they are aimed and, like film cameras, this dictates the level of sophistication and cost of the equipment. The equipment falls into a number of main types illustrated in Figure 2.2. The properties of the various camera types are summarized in later sections.

Figure 2.2 Types of digital camera: (a) ultra-compact; (b) high-end compact; (c) bridge; (d) DSLR; (e) medium-format digital camera system.

Image format

The image format describes the dimensions of the image in the focal plane. The size and spacing of individual image elements (photographic grains, or pixels) helps to define the point spread function (PSF) of the sensor (the response of the imaging system to a point of light, literally the size and shape of the reproduced image of the point), which is an important performance attribute. The combination of sensor dimensions and image element size are predominant factors in determining spatial resolution and image quality (and digital file size).

The image format also determines the size of the camera and accessories: one of the limiting factors of a lens is its covering power. When light is imaged through a lens there will be an acceptable circle of illumination formed, outside of which there is rapid fall-off illumination and natural vignetting occurs. Within the circle is another circle, called the circle of acceptable definition. This defines the physical extent of an image through the lens that will be sharp and conform to some measure of acceptable objective image quality. The diameter of the circle of acceptable definition must cover the diagonal of the image format (see Figure 2.3). This, together with the required field angle of view, defines the focal length of any type of lens for a particular format. As shown in Figure 2.4, the larger the image format, the longer the focal length of the lens for a particular field angle of view. This has a bearing on a number of characteristics of the overall system. It also has important implications in terms of the focal lengths used in digital systems, discussed later.

Figure 2.3 Lens covering power – the inner circle of acceptable definition defines the covering power of the lens. Its diameter must be equal to the diagonal of the image format.

Figure 2.4 Standard lenses: lens covering power, image format and focal length. The smaller the image format, the shorter the lens focal length needed to give the standard field angle of view.

Traditionally, film camera systems have a standard focal length lens specific to the image format (see Chapter 3 and Figure 2.4). This lens is the one providing a field angle of view of somewhere between 45° and 57°. The degree of refraction required to produce this angle results in an image close to that perceived by the human visual system. This means that the relative size of and perspective between objects within the images will be least distorted and closest to the way in which the original scene was perceived. The focal length of the standard lens will be determined by the angle of view. Fisheye, extra-wide-angle and wide-angle lenses are shorter in focal length and telephoto lenses longer than the standard lens for the particular format.

Digital sensor sizes versus film formats

One of the initial problems in producing digital cameras with comparable image quality to film was the difficulty and expense in manufacturing sensors of equivalent areas. Many smaller format digital cameras have sensors which are significantly smaller than 35 mm format film. The sizes are often

Figure 2.5 Dimensions of typical film formats and digital image sensors.

expressed as factors, and they are based on the diagonal of a 1 inch optical image projected on to a sensor by a lens, which is close to 16 mm. Examples of the actual dimensions of some image sensors are shown in Figure 2.5, compared to typical film formats.

As explained in the section above, the small sensor sizes mean that in many digital cameras the focal lengths of lenses are significantly shorter than in film-based systems. This has a number of implications. First of all, it means that in the compact market, it has been possible to make much smaller camera bodies than possible with film cameras, and this is the reason that miniature cameras have proliferated (it has also made the tiny cameras used in mobile phones a possibility – see later).

A further implication of the smaller sensors is that lenses of focal lengths designed for film formats will produce a smaller angle of view when placed on a digital camera with a smaller sensor. This means that standard focal length lenses effectively become telephoto lenses (see Figure 2.6). This issue affects small-format SLRs, where lenses from the equivalent film format might be used, and also the larger formats when using digital backs with a smaller imaging area than the associated film back. It can also cause confusion when comparing the zoom lenses of two cameras with different-sized sensors. Equivalent focal length is sometimes quoted instead, which expresses the focal length as the same as a focal length of a lens on a film camera, usually 35 mm, based on an equivalent angle of view. Alternatively, as described in Chapter 3, the ‘crop factor’ may be given, which is a factor used to multiply the lens focal length to get its effective focal length.

Furthermore, as described in Chapter 3, depth of field will be greater for a digital single-lens reflex (DSLR) with a smaller sensor than for the 35 mm film format when using a lens of equivalent focal length at the same aperture. This is because equivalent focal length is achieved when the two lenses provide the same field angle of view. For the DSLR, as described above, the focal length will be shorter. The result of this is that using a shallow depth of field for selective

Figure 2.6 Using a lens designed for a 35 mm film camera with a DSLR with a smaller sensor. The image coverage is reduced as a result of a smaller angle of view with the digital sensor. A standard lens is effectively converted to a telephoto lens.

focus on a subject is much more difficult in digital photography, because more often than not everything in the frame appears sharp. This is one of the reasons that professionals often prefer a full-frame sensor (i.e. one of the same size as the equivalent film format), because in this case the lens focal lengths and depth of field will be the same as for film.

The role of the camera in the imaging process

While the basic features of cameras described above are the same regardless of the type of sensor used (film or digital), at a quite fundamental level the function of the camera is different.

Film cameras

A photographic (silver halide) emulsion produces a latent image when exposed to light, i.e. an image that is not yet visible but has the potential to be developed and rendered permanent. In this case, the sensitive material (the emulsion) fulfils both capture and storage functions in the imaging process. To create a viewable image, the exposed film must be removed from the camera and go through a series of chemical processes to amplify and fix the image. The film is exposed frame by frame at the focal plane, and necessitates a means of either removing a single sheet of film from the camera, or winding the film on if using roll film.

The choice of camera design determines the image format, the way in which the image is captured and the range of accessories available. Image shape is controlled by choice of lens and viewpoint. However, other characteristics, such as sensitivity, noise, resolution and the tone and colour reproduction of the final image, are controlled or heavily influenced by the selection of film and the way in which the film is treated post-capture; they are quite separate from the camera.

The primary role of the film camera is therefore as an exposure device only – the camera features can be quite basic, limited only to those necessary to control exposure. Of course, many film cameras, particularly recent compact cameras and SLR cameras, are highly sophisticated, incorporating a central processing unit (CPU) to enable, for example, sophisticated methods of through-the-lens (TTL) exposure metering, focusing and fash control. It is of interest to note, however, that the larger the format of film and therefore the camera, the fewer the camera controls that are typically available. Large-format film cameras do not commonly include a built-in light meter, requiring total manual control and a separate hand-held exposure meter.

Digital cameras

In contrast, a digital camera is much more than a capture device, because the image sensor is an integrated and fixed component. Current digital cameras contain one of two types of light-sensitive array, either a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor. The optical and mechanical systems of digital and film cameras are similar, but digital cameras are more complex in terms of user controls and image processing in the camera software and firmware. Within the camera, the captured image signal must be transported off the sensor and digitized, before being processed and made permanent, by saving the data to a suitable image file format.

Because image characteristics cannot be altered by removing and replacing the sensor, as for film (although digital backs on medium format are removable), certain properties are fixed at capture, although some changes may be made to the image post-capture. For example, the pixel count of the image is ultimately limited by the pixel resolution of the sensor, but this may be artificially changed by interpolation. (It should be noted that pixel resolution is not the same as spatial resolution, although the two characteristics are interdependent; the term ‘resolution’ is often used for both - see later in the chapter). The sensor also has a native sensitivity to light, equivalent to the ISO speed of film. To accommodate the huge variation in lighting conditions, the signal from the sensor is processed and gain is applied (a form of signal amplification) to change the apparent ISO speed. Similarly, white balance, the correction of the camera response for scenes of different colour temperature, is commonly achieved by processing of the image signal. It is important to understand in both cases that the original sensitivity of the sensor remains the same. The differences are made by processing the signal post-capture.

The digital camera therefore performs several functions: capture, processing and storage, with different subsystems for each. The optical and mechanical components, such as the lens, shutter system, autofocus and exposure meter, are controlled by a camera system controller in a similar manner to those in film cameras. The analogue front-end of the camera consists of the image sensor, an analogue pre-processor and an analogue-to-digital converter (ADC). These initially store the image in the form of an electronic signal, read it off the sensor, and process it before converting it to a digital signal. Finally, the digital signal processor (DSP) processes and compresses the image (if required) before saving it in a suitable image file format. The three subsystems are illustrated in Figure 2.7, a block diagram of a generic digital camera.

Figure 2.7 Block diagram of a generic digital still camera.

Features of digital cameras

The image sensor

Instead of exposing on to silver halide-coated film, currently the majority of digital cameras contain one of two types of light-sensitive array, either a charge-coupled device (CCD), which is common in earlier digital cameras, or fast overtaking it, the complementary metal oxide semiconductor (CMOS) image sensor. The sensor is in the same position as the film in an analogue camera. Many of the key external features of digital and film cameras are similar, but digital cameras have a whole other layer of complexity in terms of user controls in the camera software.

Both types of digital image sensor are based on the same material, silicon, which when ‘doped’ with minute amounts of other elements can be made sensitive to light. When exposed to light, it produces a small amount of electrical charge proportional to the amount of light falling on it, which is stored, transported off the sensor, converted into a stream of binary digits and written into a digital image file. The process is a complex one, and the structure and operation of the sensor is covered in more detail in Chapter 6.

As described earlier, the quality and resolution of the image is primarily affected by the properties of the sensor, in terms of sensor dimensions, pixel pitch and pixel dimensions. Furthermore, the number of pixels at input will ultimately affect the reproduction of the image in terms of its dimensions at output.

Resolution and image sensors

Where resolution in traditional film-based imaging is well defined, the different ways in which the term is used and its range of meanings when referring to digital systems can be confusing. It is helpful to understand these differences and to be clear about what resolution means at different stages in the imaging chain. You will see the term explained and used in different contexts throughout this book.

The word ‘resolution’ is often used to describe the number of pixels in a digital image, or the number of pixels captured by a sensor. Strictly, this is not spatial resolution but pixel resolution. It is important to note that pixel resolution is not an indicator of the level of detail captured and reproduced in the image unless considered in the context of the PSFs of the various devices in the imaging chain. Pixel resolution may be given as a pixel count, calculated by number of rows × number of columns of pixels and referred to in terms of megapixels; this is a value often quoted by digital camera manufacturers. Pixel resolution may also be measured as a function of distance, e.g. pixels per inch (ppi). Pixel resolution is not meaningful unless considered with the dimensions of the image sensor, or the resolution of the output device.

A clever trick that manufacturers often use to enhance the apparent characteristics of their devices is to quote interpolated resolution. This applies to scanners in particular. The actual (or optical) resolution of a device is defined by the number of individual elements and their spacing; however, it is possible to rescale an image by interpolating values between the actual values, in effect creating false pixels. The visual effects of this are a slight blurring of the image, because the interpolation process averages adjacent pixels values to create the new pixels (see page 236).

Spatial resolution is the capability of an imaging system to distinguish between two adjacent points in an image and is a measure of the detail-recording ability of a system. In any imaging system this is affected by the PSF of every component through which light passes; the lens and the sensor will be the key influencing factors, but anything placed over the lens or sensor, such as a filter, will also affect it. It is usually the resolution of the capture device that is the ultimate limiting factor in the imaging chain. There are a number of measures of spatial resolution, but two commonly used and covered in more detail in the chapters on lenses and film are resolving power and modulation transfer function (MTF).

The pixel resolution or megapixels of the sensor can be very misleading when used as a figure of merit to compare different cameras, as it tells us little about the PSF of the sensor, and therefore the spatial resolution and image quality. It also provides no indication of the quality of optical components in the camera; 10 megapixels on a DSLR is significantly different in terms of results produced to 10 megapixels in a camera phone, for example.

The pixel size is important to various image characteristics affecting image quality. It seems counter-intuitive, but it is important to understand that smaller pixels do not necessarily equal better quality; there is a lower useful limit to pixel size. This is because at very small pixel sizes (sensors in digital compact cameras may have pixels of 1.4 µm²) the saturation level (maximum response) of the pixel will be limited (due to the reduced imaging area). This restricts the dynamic range and the noise levels associated with the signal may start to become significant. It is one of the reasons that full-frame DSLRs and medium-format cameras have larger pixels. The results are quite obvious in terms of reduced noise and improved dynamic range. These issues are covered further in Chapter 6.

How many pixels?

When buying a digital camera, pixel resolution is a primary consideration, and a key factor in image quality; however, the previous discussion indicates the confusion around the subject. The highest number of megapixels does not necessarily represent the highest quality or automatically mean that the largest level of detail will be reproduced. It is much more important to consider the number of effective pixels in the context of the sensor size, which gives an idea of pixel size. These and other factors, detailed below, are involved in determining the PSF of the sensor and various image characteristics important to image quality.

The pixel pitch, which is the centre-to-centre distance between pixels and relates to the overall pixel size, is the sampling distance and is an important aspect of spatial resolution, as well as determining the maximum frequency of a periodic pattern that may be accurately reproduced without causing aliasing (see the later chapter on image sensors). However, the image-sensing area of each pixel in some cameras may be as low as 20%, due to the inclusion of other components and wiring at each pixel and channels in between imaging areas.

The pixel shape is also important; some sensors use non-square pixels to improve various aspects of image quality (the Fuji Super CCDs are an example, using hexagonal pixels to reduce horizontal and vertical pixel pitch) and these will affect the shape of the PSF. The interpolation algorithms used in calculating missing colour values (demosaicing – see below), which vary between manufacturers, will also have an effect on final image resolution. These

Figure 2.8 Sensor resolution, dimensions, file sizes and printed dimensions.

factors combine to influence the shape of the sensor’s MTF; this is a far better indicator of how well a camera will perform. The quality of the lens must additionally be taken into account.

These issues point to the fact that you should not make a choice based solely on the number of megapixels. Make informed decisions instead, based on results from technical reviews and from your own observations through testing out different camera models. You need to decide beforehand how you want to use the camera, for what type of subjects, what type of photography and what type of output.

Bearing all this in mind, it is still useful to have an idea of the physical size of output images that different sensor resolutions will produce. Print resolution requirements are much greater than those for screen images. Although it is now widely accepted that images of adequate quality can be printed at 240 dpi, or perhaps even lower, a resolution of 300 dpi is commonly given as required output for high-quality prints. Some picture libraries and agencies may, instead of specifying required image size in terms of output resolution and dimensions, state a required file size instead. It is important to note that this is uncompressed file size. It is also necessary to identify the bit depth being specified as this will have an influence on file size. Figure 2.8 provides some examples for printed output.

Colour capture and demosaicing

As described in Chapter 6, nearly all colour capture in digital cameras is achieved using a single sensor overlaid with a colour filter array (CFA). The most common arrangement is known as the Bayer array, illustrated in Figure 2.9, consisting of RGB filters, with twice the number of green filters to blue or red. There are a number of other types, using various combinations of primary or complementary filters, some of which are also illustrated in Figure 2.9.

At each pixel, the light reaching the sensor will contain only the range of wavelengths transmitted by the filter, producing a single value. This will correspond, usually, to the value of a single channel, depending on the filter arrangement. To obtain the missing values for the other colour channels at that position, the values will need to be interpolated from their neighbours, usually using some form of bilinear interpolation. This process, which is necessary to produce a full RGB image, is known as demosaicing. It is necessary to produce a fully colour rendered and viewable image (see page 151 for more details on demosaicing). Prior to demosaicing, the image is in the form of RAW data. Commonly, demosaicing is performed in the camera in the digital signal processor (DSP). However, as described in later sections, in professional workflows it is becoming more common to output RAW data from the camera, bypassing much of the on-board camera processing. This affords the photographer significantly more control over the image, as it is processed and demosaiced in a separate application with the user able to preview and adjust the results. Demosaicing, like any interpolation process, causes a certain amount of blurring. Therefore, almost all digital cameras incorporate some form of sharpening to counteract this, and other sources of blurring in the imaging pipeline.

Figure 2.9 Different types of colour filter arrays used in image sensors: (a) Bayer array; (b) complementary mosaic pattern; (c) RGBE filter pattern (Sony); (d) example RGBW filter pattern (Kodak) – R, red; G, green; B, blue; C, cyan; M, magenta; Y, yellow; E, emerald; W, white (transparent).

Other optical components

The structure of digital image sensors, in terms of the regular non-overlapping arrangement of pixels, and the spectral characteristics of the doped silicon necessitate a number of additional components in front of, or incorporated with, either the sensor or the lens. These include:

1. Infrared (IR) filter. Usually an IR absorption filter, this is placed between lens and sensor, sometimes attached to the rear surface of the lens. The filter blocks out IR radiation, which doped silicon has a natural sensitivity to (see Chapter 6). Certain applied imaging applications, such as forensic imaging and clinical photography, use techniques in which images are produced from IR radiation refected from subjects. Where traditionally they would have used expensive IR-sensitive films, professionals are now able to use DSLRs with the IR filter removed (see Chapter 11). To this end, some manufacturers have made the IR filter relatively straightforward to remove (although it is still a delicate process). Furthermore, one or two manufacturers of DSLRs have produced versions without the IR filter specifically for scientific use.

2. Anti-aliasing filter. As explained earlier, a characteristic of the spatial sampling process is aliasing, an artefact caused when a regular (periodic) pattern is undersampled. This causes the well-known moiré artefacts seen when any finely spaced regular pattern (such as stripes or checks) is imaged on television and can cause jagged artefacts on diagonals in digital images, as well as colour artefacts (see page 160). It is characteristic of any sensor which samples a scene at regular intervals. The effect can be reduced using an anti-aliasing filter, an optical filter that effectively blurs the very fine details likely to be aliased. The anti-aliasing filter is placed in front of the sensor. The blurring effects, like those caused by interpolation processes, must be counteracted by image sharpening later on. See also Chapter 8.

3. Micro-lenses. As the name suggests, these are tiny lenses which are attached to the surface of each individual sensing element on the sensor and help to focus the light into the centre of the pixel, reducing light losses. You can read more about micro-lenses in Chapter 6.

Image processing

Digital image capture is a complex process. The signal from the sensor undergoes a number of processes before it is finally written to an image file. The processes are carried out either on the sensor itself, in the camera’s built-in firmware or via camera software, in response to user settings. They are designed to optimize the final image according to the imaging conditions, camera and sensor characteristics, and output required by the user. The actual processes and the way they are implemented will vary widely from camera to camera. Some are common to most digital cameras, however. They will be covered in more detail in other chapters, but are summarized below. Some are sensor specific, in-built and not user controlled, often implemented in firmware. They include:

• Signal amplification. This may be applied to the signal before or after analogue-to-digital conversion; this is a result of auto-exposure setting within the camera and ensures that the sensor uses its full dynamic range. In effect the contrast of the sensor is corrected for the particular lighting conditions.
• Analogue-to-digital conversion. This is the process of sampling and converting analogue voltages into digital values.
• Noise suppression. There are multiple sources of noise in digital cameras. The level of noise depends upon the sensor type and the imaging conditions. Adaptive image-processing techniques are used to remove different types of noise. Noise is enhanced if the camera gets hot (the sensor is sometimes cooled to reduce the noise levels), also if long exposures or high ISO settings are used.
• Unsharp mask filtering. This is used to sharpen edges and counteract blurring caused by interpolation.
• Colour interpolation (demosaicing). This is the process of calculating missing colour values from adjacent colour-filtered pixels.

Additionally, settings by the user may implement processes controlling:

• White balance and colour correction. The image colours (the gamut) are shifted to correct for the white of the illuminant and ensure that neutrals remain neutral. White point setting may be via a list of preset colour temperatures, calculated by capturing a frame containing a white object, or measured by the camera from the scene. In film cameras, this requires a combination of selecting film for a particular colour temperature and using colour-balancing or colour-correction filters.
• Tone and gamma correction. The tonal range captured on the sensor is corrected to ensure that it appears visually accurate. This is because the sensor produces a response which is directly proportional to the amount of light falling on it (i.e. a linear relationship), but the human visual system and many other digital devices, such as display devices, do not. Gamma correction alters the captured values so that they are displayed correctly on display devices and appear visually correct, i.e. equal steps between consecutive tones (greys) appear visually equal. Tone correction may also be used to produce a more pleasing tonal range, changing the contrast in the shadows, mid-tones or highlight ranges, to more efficiently make use of the available dynamic range.
• Appearance characteristics. Both tone and colour correction may be applied to produce an image with a particular ‘look’, for example where a ‘portrait’ setting has been used. These are presets which manipulate the rendering of the image to produce particular characteristics in terms of tone reproduction and colour gamut. Such settings tend to be more common in smaller format cameras, compacts or semi-professional DSLRs.
• ISOspeed. The sensitivity of the sensor is set by amplifying the signal to produce a required range of output values under particular exposure conditions. Again, in film cameras, this would be achieved by changing to a film of a different ISO. ISO settings usually range from 100 up to 800. Some cameras will allow ISO values up to 1600 or even 3200. The native ISO of the sensor, however, is usually 100-200. Anything above this is a result of amplification. Amplifying the signal also amplifies the noise levels and this may show up as coloured patterns in fat areas within the image.
• Exposure and the image histogram. Exposure measurements are taken through the lens as for a film camera and image processing takes care of the rest. To optimize this process the image histogram is provided in SLRs and larger formats to allow exposure compensation and user adjustment. This is a graphical representation, a bar chart of the distribution of output levels, and is an accurate method of ensuring correct exposure and contrast, as viewing the image in the low-resolution and poor viewing conditions of the LCD preview window may produce inaccurate results. In particular, it can be difficult to tell in the preview when highlight values are clipped, a situation to be avoided. The histogram will easily alert you to this and allow you to make necessary adjustments for a perfect exposure. For more information on exposure and the histogram, see Chapter 8.
• Image resolution. Many cameras will allow a number of resolution settings, lower than the native pixel resolution of the camera, to save on file size. These lower resolutions will be achieved by down-sampling, by interpolating values from the existing sensor values.
• Capture into a standard colour space. With the necessary adoption of colour-managed workflow, a number of standard colour spaces have emerged. Capturing into a standard colour space means that the image gamut has the best chance of being reproduced accurately throughout the imaging chain (see Chapter 8 for further details). The two most commonly used standard colour spaces in digital cameras are sRGB and Adobe RGB (1998). sRGB is optimized for images to be viewed on screen. The slightly larger gamut of Adobe RGB encompassed the range of colours reproduced by most printers and is therefore seen as more suitable for images that are to be printed.
• File quality (if image is to be compressed) and file format. Most cameras will offer a range of different output file formats. The most common ones in digital cameras are JPEG, TIFF and RAW formats. The merits of these different formats are discussed in detail in Chapter 8. Of the three, JPEG is the only one that compresses the image, resulting in a loss of information. A quality setting defines the severity of the loss, file size and resulting artefacts. TIFF and RAW are uncompressed and therefore file sizes are significantly larger. TIFF is a standard format that may be used for archiving images without loss. RAW is more than a file format, as it results in almost unprocessed data being taken from the camera. With RAW images, the majority of the image processing detailed above is performed by the user in separate software after the image has been downloaded from the camera.This short summary highlights some of the differences between using film and working digitally. The immediacy of results from digital cameras is somewhat counterbalanced by the number of settings required by the user before image capture. However, it also highlights the high degree of control that you have. Many of the adjustments that would have to be performed optically with a film-based system, or by changing film stock, may be achieved by the flick of a switch or the press of a button.

Camera types: analogue and digital

Using a particular camera format has implications in many areas for the photographer: in the quality of the final image, the portability of the equipment, versatility of use, the maximum aperture of the lenses, and importantly in the cost of both equipment and film. These factors influence the way in which the photographer works at every level. Ultimately the system and format they select will determine – or be determined by – the type of photography in which they specialize.

The camera system defines the design and complexity of the camera, the degree of control by the user, the method of use and the type of accessories available. As briefly described in the earlier section on camera design, analogue and digital cameras can be broadly categorized into a range of different types. This section explains the properties of the main types in more detail. Apart from the sections below on mobile phone cameras and digital compact cameras, which make up such a large part of the amateur market, it is based on the three main types used in the professional market, which originate from the relevant film formats, but now have digital equivalents and variations.

Point-and-shoot cameras

Predominantly aimed at consumers and making up the largest part of the market, compact digital cameras grow ever more sophisticated, with increasing sensor sizes, improved image processing, and an emphasis on features to enable new modes of imaging and facilitate modern methods of communication and transmission of images. They tend to have the largest range of automatic and programmed modes and often incorporate digital video capture. Mobile phone cameras – with fewer features and lower quality optics – can also be included in this category. Ultra-compacts, popular with consumers, exploit the fact that small sensor sizes mean that the camera body and lens focal lengths can be reduced to produce ‘pocket-sized’ cameras. At the top end of the price range are Prosumer compacts, which with higher quality optics, larger sensors and the option of RAW capture are marketed at the serious amateur or at the professional photographer.

Mobile phone cameras

At the lowest end of the market are mobile phone cameras. Pixel counts of up to 10 megapixels on sensors in mobile phones are now beginning to rival and surpass those in the compact point-and-shoot cameras of a few years ago. Furthermore, a 14 megapixel CCD camera phone, with 3× optical zoom and video, has recently been announced, for launch in Europe in early 2011.

CMOS image sensors were first used in mobile phones; at the time the noise levels and low resolution associated with CMOS were unacceptable for other cameras, but the advances in the sensors in terms of both smaller pixel sizes and improved noise suppression have meant that image quality has steadily improved. The optics on mobile phone cameras tended to be low quality, often plastic, although they have recently improved; however, this is of much less importance bearing in mind the way in which these cameras are used.

Interestingly, mobile phone cameras are currently the fastest growing part of the digital camera market. The improvement in sensor pixel resolution, optical components, image processing and connectivity of mobile phone cameras has meant that they have, to some extent, ended up competing with the digital compact market, simply because they are incorporated into a multifunctional device. In recent years it has become common to see mobile phone still images and video footage sent in by the public, used in newspapers and television reports, where it would not have been possible to obtain such images unless a journalist had been on the scene. Their development and use has been further fuelled by the expansion of social networking applications such as Facebook, where a mobile phone is a much more convenient way to upload images.

Digital compact cameras

There are a huge variety of compact cameras available, with many of the features typical on film compact cameras, such as built-in fash, a large variety of exposure and shooting modes, including movie modes and red-eye reduction. There has been a trend towards miniaturization by some manufacturers, resulting in ultra-compact cameras, which are truly pocket sized. This has been aided by the ease of producing small CMOS sensors and the fact that many have scrapped viewfinders in favour of viewing the image on the LCD screen at the back. The other types of compact commonly available look more like an SLR, but tend to have smaller sensors. Nevertheless, recent models have sensors of between10 and 14 megapixels. Both types tend to be more automated, often without manual options. They may also only have digital zoom rather than optical zoom and output still image file formats may be limited to JPEG only. Prices are widely variable and continually coming down. The shelf-life of a particular camera model continues to decrease; often the next version in a successful range will be out six months after the last.

At the top end of the compact market are a couple of cameras aimed more at the professional (see Figure 2.2(b)) – the point-and-shoot for the professional photographer. They are significantly more expensive than the majority of compacts, up to three times more than those at the cheaper end, but have fewer automated features, some without zoom lenses and a number of models with interchangeable lenses and accessories. They allow manual setting of most features; capture to RAW file format and sensor resolutions rival those of some SLRs. The cost is in the build quality, the sensor and the optics. They are sometimes marketed as Prosumer (Professional consumer) compacts.

Properties of small-format cameras

Small-format cameras sell to a huge market of amateurs as well as professionals, and probably represent the best value for money because prices are highly competitive. Compared to medium and large formats, these cameras have moved furthest away from traditional mechanical operation towards more and more electronic control, on-board processing and in some cases complete automation. The small format means that the camera body is smaller and less bulky than medium-format or large-format view cameras, and so it is the most portable. Using equipment of this size means that you can carry around a comprehensive outfit in a small case. There is an unrivalled range of lenses and accessories available, and the whole system will incorporate the very latest developments in technology.

The majority of small-format cameras, analogue or digital, are single-lens reflex (SLR) cameras, although in recent years a type of hybrid digital camera, known as the bridge camera, has appeared (Figure 2.2(c)). These tend to have large-range zoom lenses rather than interchangeable lenses and they do not usually incorporate a single-lens reflex viewfinder, instead employing live preview on an LCD display. Bridge cameras, as the name suggests, are aimed at providing a bridge between the features of digital compacts and DSLRs.

Figure 2.10 Small-format DSLR camera andaccessories.

Generally more expensive than bridge cameras and aimed at the serious amateur, the ‘semi-professional’ SLR is also known as a Prosumer SLR camera. These SLRs tend to have more of the features of the professional ranges, with body designs which are very similar, but they are cheaper, often the lower price resulting in a compromise in build quality and lens performance. Prosumer SLR cameras tend to be the ones with the most programmable and automatic features. These models are updated quite rapidly and bristle with every conceivable feature. This ‘bells and whistles’ aspect is sometimes more to upstage rival brands than to improve your photography.

One of the useful features small-format cameras tend to include as standard is through-the-lens (TTL) exposure metering. This of course means that the whole imaging process is faster than it would be if separate exposure metering were required. Metering can be performed while looking through the viewfinder and, in many cases, the camera controls are designed to be easily altered in this position. Modern SLRs often include a number of TTL metering modes, such as centre-weighting and spot metering, and with knowledge and experience the most difficult subjects can be correctly exposed. This is a factor that really defines how the cameras are used; they are portable, all-in-one units, allowing the user to capture fleeting shots without spending a long time setting things up. Although they may indeed be used in a studio setting, where there is time and space to get everything right, they are also designed for all other types of photography and they far surpass the other formats in their versatility. Many small-format ranges also include dedicated fash units and, at the more expensive end, these may include TTL fash metering. Indeed, later models of independent fash units may also be adapted to use the TTL metering systems of small-format SLR cameras. This is a huge bonus when using on-camera fash and is particularly useful in photo-journalism.

Depth of field is affected by a number of factors, such as focusing distance, selected aperture and, importantly, lens focal length. Shorter lens focal lengths produce a larger depth of field, especially useful when subjects are close. Another important characteristic of shorter focal length lenses is wider achievable maximum apertures (f/1.0–f/1.4 at the more expensive end of the market); therefore, the lenses are also faster. The result of this is that they are the most versatile in low-light-level conditions. The smaller camera size means that they are already the most portable, but with faster lenses, they are also the easiest to hand-hold in existing light, meaning that fewer accessories such as tripods and additional lighting may be necessary. Large apertures also allow the selection of faster shutter speeds to freeze motion, particularly important in areas such as sports photography.

As previously highlighted, modern small-format cameras tend to rely heavily on electronics to control everything from exposure metering, ISO setting, exposure compensation and bracketing to sophisticated program modes. A downside of this is the possibility of camera failure either as a result of failure of the power supply, or because of a fault in on-board circuitry, which can be expensive to repair. Excessive control buttons or, alternatively, total automation can also be counterproductive for serious work. The many mode options and viewfinder signals get in the way, even lead you into errors – perhaps through mis-selection or distraction by data displays at the key moment of some fleeting shot. Any camera for advanced amateur or professional work must also offer complete manual control. You need to have the assurance that you can take over and make use of your personal experience to get exactly the result required, including chosen effects.

A fully automated camera is well worth considering, however, for fast, candid photography (including situations where you must shoot over your head in a crowd). Autofocusing can be useful, particularly if panning and focusing on a moving subject, but it is important to remember how power-hungry continuous focusing is. There can also be a tendency for the focus to slip between different subjects and it can sometimes be easier to change focus manually. The more sophisticated models have a range of autofocus zones within the frame, which are useful if the subject is off-centre. Some of the highest quality (and of course most expensive) lenses have ultrasonic image stabilizers to combat camera shake, which can result in a huge improvement in image quality, but as this is also a form of continuous autofocusing, they will eat up your camera batteries.

Semi-professional DSLRs

These cameras are hybrids, with many of the automatic features of compact cameras but with more of the manual controls available with SLRs. Where professional SLRs may be sold as camera body only, these tend to be marketed as all-in packages. Currently they do not include full-size sensors, i.e. of equivalent size to the film format, meaning that they incorporate lenses of shorter focal length than equivalent for a 35 mm film SLR. Actual sensor sizes are variable (see Figure 2.5). They may have a range of interchangeable lenses and a variety of accessories available, and are sometimes compatible with the lenses from the equivalent film cameras (with an associated crop factor). The lenses sold with them are of lower quality than the professional ranges. This is not to knock them, however; some of the hybrid cameras produced by manufacturers such as Canon and Nikon in recent years contain sensors that surpass the performance of those in professional ranges of a few years ago.

They are aimed at the serious amateur and their price refects their hybrid status, being significantly more affordable, sometimes half the price (including lenses) of the professional equivalent (body only).

Professional DSLRs

These cameras are the closest to conventional film formats and are aimed at the professional. The camera bodies are almost identical in design, apart from the image sensor and related optics, processing and the LCD screen on the back. Some manufacturers have even maintained the position of the main controls to make the transition from film to digital even easier. Often sold as a camera body only (although some may come with cheaper lenses), they are designed to replace the film camera body in a professional kit, without requiring additional lenses or accessories. They tend not to have the array of automatic features of their semi-professional counterparts, with fewer modes and more manual control. These cameras have been widely adopted by photo-journalists, in particular sports photographers, who often carry laptops as part of their kit and are able to download, crop and adjust their images before sending them wirelessly to their picture editors within a matter of minutes. In these types of photography, speed is of the essence and can mean the difference between your images, or someone else’s, being used and syndicated.

At the top end of the range of professional DSLRs, sensors are full frame, the same image size as 35 mm format, meaning that lenses are of the same size as the film equivalent. There is a significant hike in price to refect this, in part due to the difficulty in manufacturing larger area sensors, but also because they are currently very much aimed at professionals, and therefore have superior build quality, features (e.g. dynamic range, image processing), lenses and accessories. At the time of writing sensor pixel resolutions have an upper limit of around 25 megapixels, giving an output file size of nearly 70 MB.

Film SLRs

Often termed 35 mm cameras, film SLRs use roll film with image dimensions of 24 × 36 mm. As a result of the small image format, lenses for 35 mm camera systems are the shortest compared to the other film formats, with a standard lens of focal length 50 mm, telephoto lenses longer than this, wide-angle lenses beginning at around 24 mm and extra-wide-angle lenses at 20 mm and below.

Because film structure is the same regardless of frame size or format, image quality is an important consideration. Film grain is the result of either specks of silver (black and white) or clouds of dye (colour) being formed in the emulsion layers during processing. When enlarged for printing, beyond a certain level film grain becomes apparent. The random structure of the film grain can be used for creative effect, but it can also degrade the image appearance in terms of sharpness and noise. The size of developed grains is also a limiting factor in the spatial resolution of the film. Relative to a 35 mm frame size, film grain will be much larger than it is in the larger formats; 35 mm film therefore has the lowest effective resolution of the three, which means that if enlarged to the same size as a frame of medium- or large-format film, the images will be less sharp, grain will be more evident and generally they appear to be of lower quality. Scratches and blemishes will also be much larger when the film is printed and perhaps more difficult to remove. The lower image quality may be problematic if the images are enlarged much beyond 8 × 10 in. (203 × 220 mm); however, other factors can compensate for this, such as variations in the processing chemicals, and also in the distance at which the prints are to be viewed.

Properties of medium-format camera systems

Medium-format cameras tend to dominate in many other areas of professional photography, where image quality is a priority. They represent a good compromise between the size and quality of the image produced by their large-format counterparts and the versatility of use of small-format SLRs. The medium-format market is quite different to that of small-format cameras. The cameras require more skill in use and are not as portable; therefore, they tend to appeal more to professionals, who are usually prepared to invest more in a camera system. As a result of this, the market is less competitive, with fewer manufacturers and a limited range of different models. Further, the larger format image requires lenses of higher quality, so generally these systems are larger and significantly more expensive. Features tend to be more conservative, and because of the small numbers manufactured you can expect to pay over twice the price of an equivalent small-format kit. Where the competition among small-format camera manufacturers has lead to the development of many gimmicks and automatic features, medium-format cameras tend to be simpler in design and rely more on mechanics than electronics. The increase in cost is in the quality of components and the camera build.

Medium-format cameras are small enough to use hand-held and cope with action subjects. You can use most types at waist or eye level – there are a range of direct viewfinder wide-angle models as well as reflexes (Figure 2.11). At the same time, shift cameras (Figure 2.12) and monorail view cameras are now made for medium formats.

The standard lens for medium format is generally an 80 mm focal length. If you are used to working with smaller formats the shallower depth of field given by the longer focal length lenses normal for medium formats can be an unwelcome surprise – especially when shooting close-up. Lenses also have maximum apertures one or two stops smaller than their small-format camera equivalents (typically, f/2.8 or f/4 for a standard focal length lens), meaning that although they can be hand-held, they require relatively bright conditions. The longer lens also means more camera shake, so a tripod is usually a necessary accessory.

Figure 2.11 There are a range of different camera designs available in medium-format cameras for general work.

Figure 2.12 Medium-format cameras providing camera movements. Top: scaled-down monorail design accepts rollfilm magazines, instant picture or digital backs. Bottom: bellowless wide-angle shift camera for architectural work offers rising and drop front, and accepts rollfilm backs.

Medium-format film camera systems

There are a range of image formats available for medium-format cameras. The films are mainly 120 mm wide and the most common image formats are 60 × 45, 60 × 60 and 60 × 70 mm. They are available as sheet film but are mainly used as rollfilm. The range of film stocks made in 120 rollfilm is more limited, with the emphasis on professional rather than amateur emulsions. Since rollfilm picture size is between three and five times the area of 35 mm, you can crop after shooting if you wish and print (or reproduce) from just part of the image without too much lost quality. An SLR this size also has a screen large enough to usefully attach a drawn overlay for critical jobs where your composition must ft a tightly designed layout. Here the camera designs allow more versatility than 35 mm. When using a roll of 35 mm it is usually necessary to shoot the entire roll before the film can be changed. The alternative is to rewind the shot part of the film, change films and then, when ready to use the film again, it is necessary to wind it on to the point at which it had been wound to before. As well as being inconvenient, this is fraught with difficulties, often resulting in gaps of unused film which is wasted, or in double exposure of frames due to incorrect guesswork. Many medium-format cameras solve this problem with detachable, interchangeable film backs, meaning that different types of film can be loaded during a shoot, without any of the hassle of rewinding, so you can be shooting using one film back while an assistant is quickly emptying and reloading another, allowing fast, continuous photography. You can also shoot one scene on several different kinds of film stock by juggling backs. It is a facility which permits you to swap to an instant picture (peel-apart) back at any time during a shoot to visually check on lighting or exposure. Many professional-type rollfilm cameras will accept digital backs too.

Medium-format camera systems have the widest range of different viewing systems. They include twin-lens reflex (TLR) designs (Figure 2.1(d)), which have a viewing objective separate to the imaging objective and waist-level viewfinder containing an angled mirror and a focusing screen. SLR designs are more common, where the viewing lens is also the imaging lens. For SLR cameras, the viewed image is projected via a reflex mirror into the viewfinder, which has to be moved out of the way prior to exposure, blacking out the viewed image. The movement results in a slight shutter lag and can lead to slight camera shake, although the mirror can often be locked up to prevent this. TLR cameras do not have these problems, as the lens is separate. The other main type of medium format is the rangefinder camera, which is also common in smaller formats. Rangefinder cameras, as the name suggests, include a mechanism for measuring distance to subject. Like TLRs, they include a separate lens for viewing. They display two images of the subject, one of which moves, and the measured subject distance is identified once the two images coincide.

The method of exposure determination in these systems is often built in, but as already mentioned these cameras tend not to have as many features to aid the photographer as their smaller counterparts. Using them takes you back to the fundamentals of photography, with the majority of exposures made in manual mode, with manual focusing. They require more consideration in their approach. The process of loading or changing film backs, or winding on film, is more technical than the point-and-shoot and wind-on approach that might be used with 35 mm and the skills required to use them properly take time to acquire. However, once you are used to this way of working, they can be just as versatile and the increase in quality means that they tend to be preferred for high-quality print output such as that produced for magazines and books.

Medium-format digital camera systems

Digital medium-format cameras and digital backs are significantly more expensive than professional DSLRs and the medium-format film equivalent. Digital backs contain a large sensor with mounts for various medium- and large-format camera systems - in most cases the sensor is smaller in size than the equivalent film format. The first medium-format digital camera system incorporating a ‘full-frame’ sensor, equivalent in size to an approximately 40 × 50 mm film frame, was announced in July 2008 by Phase One.

Because of the cost and the lack of cameras and backs with full-frame sensors, a significant part of the market continues to use film and the manufacturers traditionally associated with the film systems continue to manufacture film magazines for use with their systems, alongside newly developed digital backs. Currently, medium-format systems use CCD sensors, although there have been recent announcements of the development of larger format CMOS sensors. Sensor sizes and pixel resolutions are variable, as they are for smaller formats. Some examples are given in Figure 2.5. Often, pixel sizes are larger than those in smaller formats, resulting in higher saturation levels and reduced noise, and leading to significantly higher dynamic range than small-format SLRs.

Digital medium format is offered by a relatively small pool of manufacturers. Various different designs exist, including:

1. New modular camera systems designed to include both film and digital backs. These have relatively large sensor sizes, often twice the size of full-frame 35 mm DSLRs and, as mentioned above, larger pixel sizes improving dynamic range.

2. Modular camera systems which are designed to work with a range of different digital backs, providing a solution across a range of image quality and cost. Sensors range from small and relatively low resolution (comparable to those currently available for 35 mm DSLR) to very high resolution and closer to full frame (an example is a 60.5 megapixel sensor of 53.5 × 40.4 mm).

3 .Digital backs designed to be incorporated into existing traditional modular systems for film by the same manufacturer. Sensor sizes and resolutions tend to be significantly smaller than those incorporated in the specially designed systems described above, but these represent a relatively cost-effective solution for a photographer who already owns a medium-format film camera system.

4. Multi-use digital backs which are designed to work with different types of camera systems. Again, with large sensors, they may be used with existing medium- and large-format view camera systems from other manufacturers.

5. Non-modular medium-format SLRs with an incorporated sensor. This part of the market is beginning to be penetrated by manufacturers not previously associated with medium format. These types of cameras offer a bridge between the expense of modular systems and 35 mm DSLRs. Because the sensor is larger than full-frame 35 mm SLR, image quality is improved, but they represent the lower cost end of the medium-format market.

Figure 2.13 A medium-format camera system with digital back.

Most of the systems described above incorporate similar features, such as viewfinder systems, lenses and accessories to their film based counterparts.

Large-format view camera systems (film and digital)

In many ways, cameras using 4 × 5 in. (102 × 127 mm) image format and upwards are a world apart (Figure 2.14). Photography with this type of equipment is more craft orientated; it demands more elaborate preparation and encourages a more considered approach to your subject. There are fewer camera designs to choose from, and both cameras and lenses are expensive - especially the 8 × 10 in. (203 × 254 mm) size. Here we concentrate on the use of large-format film. At the time of writing, this is the one area of photography where film continues to dominate. This is partly because large-format photography is a specialized niche market, but particularly because it is difficult and expensive to manufacture large area sensors (hence the prohibitive expense of medium-format digital systems described above). There are currently very few options for digital capture at large format, but these are mentioned briefly at the end of this section.

Figure 2.14 A typical 4 × 5 in. unit constructed monorail camera.

These cameras are closest to very early camera designs, incorporating a bellows extension between movable lens and film planes. Most commonly, they are attached along an axis, a monorail, allowing the distance between them to be altered; the two planes also have a range of positions and tilts that can be applied in a variety of camera movements, to manipulate the size and shape of the subject, covered imaging area, magnifcation and depth of field (see Figure 2.15 - more details on camera movements are covered in Langford’s Basic Photography). Making the most of these cameras requires skill, practise and a genuine understanding of the optical principles governing them. Most certainly not for the amateur, the image capture process is

Figure 2.15 Camera movements using a view camera. Both lens plane and film plane have a range of tilt (b, c)and swing (e, f) movements for achieving different manipulations of the image plane.

involved and time-consuming. The cameras are bulky and cumbersome, requiring a tripod, and they often lack electronic aids completely, unless you add costly accessories. Therefore, you must expect to use a separate hand-held exposure meter and calculate the exposure increase needed for bellows extension, etc., which is taken care of in other cameras by TTL light measurement. The image is inverted and viewed directly through a large ground glass screen in the position of the film plane at the back of the camera.

Because these cameras require tripods and time to set up, they tend to be used more for still-life subjects. The camera movements available and large image format allow great representation of detail and fine-tuning of image shape; this type of precision work lends itself to high-quality studio still-life photography. The other main application, for the same reasons, is architectural photography, where tilting camera movements may be used to correct converging verticals and translational movements may be used to capture the top or edges of a building that other formats would not cover.

The standard lens for a 4 × 5 in. large-format camera is most commonly 150 mm or 180 mm. The long focal length results in shallower depth of field than either 35 mm or medium format; however, if the subject allows it, tilting or swinging either front or back planes may bring required zones of subject into focus, improving effective depth of field. You must expect to stop down more and consequently require more light or longer exposures. Even maximum lens apertures average around f/4.5–f/5.6, some three to four stops slower than most 35 mm format lenses.

On the other hand, you can expect view camera lenses to have a much wider image circle than lenses intended always to be dead-centred on the film. For example, a good normal-angle 180 mm lens designed for 4 × 5 in. will give a circle of acceptable quality about 300 mm in diameter when focused for infinity and stopped down to f/22. This means that you can shift or pivot the lens until its axis is more than 70 mm off-centre if necessary for rising, cross or swing front effects before you see loss of image quality at any corner. It is a false economy to buy, say, a monorail view camera offering extensive movements and use it with an economy lens barely covering the format.

After setting up a shot, the image is usually captured on individual sheets of film, which are loaded into a sheet film holder and are then processed separately. This means that there is the same versatility as medium format in terms of being able to repeat the same shot on different film stock. Single sheets are more expensive, but the time taken in setting up means that fewer mistakes are made and less film is wasted. The range of film available is much lower than that available for other formats, but the large image size ensures that grain is finest, images are sharpest, and the tonal range and level of detail are the greatest possible.

Figure 2.16 A scanning back containing a trilinear CCD array for large-format view camera. Image courtesy of Better Light, Inc.

To work with the relatively large focusing screen of a view camera is like having upside-down colour television. The equipment brings you much closer to the optical craft aspects of photography than any smaller camera, but you must understand what you are doing. Remember, too, that a 4 × 5 in. camera with a couple of good lenses can cost you over three times the price of a professional quality 35 mm three-lens outfit.

In terms of digital photography, there are a few different large-format options. For highest quality digital images intended for big prints, larger file sizes are required. At this level, CCDs dominate. There are two main types: either frame arrays, which capture the entire frame at once; or digital scanning backs, which use a trilinear CCD array (three rows of sensors, each capturing red, green or blue (Figure 2.16)). As mentioned above, a number of manufacturers traditionally associated with medium format have produced digital backs incorporating frame arrays, which may be used with 5 × 4 view camera systems. For architectural and landscape photography, these tend to be the only suitable choice. Because the sensors are significantly smaller than the film format (note that, in the majority of cases, the sensors do not yet equal most standard medium-format film dimensions), they have reduced wide-angle capability, which is a current disadvantage.

The only other option is the use of a large-format scanning back. These are high resolution, capturing an entire large-format image by scanning down the frame using a linear sensor. A full colour image of many millions of pixels is built up line by line to give image files at the top end of the scale of over 400 MB. They are expensive and because they physically track across the camera image plane throughout an exposure, subject matter is limited to still-life studio-based work, as both camera and subject must remain still for a couple of minutes. The time lag during the scanning process also necessitates non-varying lighting conditions. Therefore, they cannot be used with fash and, when using tungsten illumination, any lighting intensity variations (such as minor flickering) must be avoided because this will show up as a band across the picture.

Clearly, dealing with such large digital files is a completely different matter compared to the convenience of using DSLR. There are huge storage requirements involved and processing must be done predominantly on a peripheral computer; therefore, digital large format is much more likely to be used in a studio setting than its analogue counterpart.

Which one is best?

Clearly, no one camera will serve you well for every kind of assignment. Some give you a choice of at least two formats – for example, the use of different format digital backs with one of the modular camera systems described above. However, the result is often an unsatisfactory compromise, with the lens too long focus and the camera unnecessarily bulky for the smaller format. Most photographers therefore opt for two camera outfits – for example, small and medium format or medium and large. Having two complementary kits means that you can exploit their advantages and minimize their individual shortcomings for the widest range of subjects. When you have made this decision go on to choose whether reflex, direct viewfinder or monorail designs (as available) will suit you best, and pick appropriate lenses.

On price, you will find that within any one category of camera the difference between cheapest and most expensive models can easily be a factor of 2 or 3 (10–12 times with small-format DSLR gear). Sometimes this extra cost is because the body has features utilizing the latest technology, or it is built with greater precision and finish, using much tougher components. Like hand-built cars, this lasting precision and reliability cannot really be seen unless you open up the inside.

Specialized accessories

You can choose from a very large range of camera accessories. Many are unnecessary and gimmicky, but some of the more specialized add-ons allow you to interface cameras with completely different kinds of technology.

Optical adaptors

Most small-format SLR camera systems include different adaptor rings which allow the camera body to ft over the eyepiece end of a microscope, telescope, medical endoscope, etc. Owing to reflex design you can still accurately frame up, focus and measure exposure whatever optical device is fitted. In fact, the camera becomes a sensor-containing back for the other device.

Camera triggers

You can buy electronic sensor units which trigger your camera in response to light, sound, radio or infrared radiation. Normally, you wire one of these devices to a small- or medium-format camera having electric release sockets plus motor drive so that any number of pictures can be taken remotely. The camera might be set up in some inaccessible position, such as under a jump on a racecourse, and then fired when you transmit an infrared or radio pulse from the safety of the trackside. For natural history photography you can mount the camera in some hidden location, its shutter triggered automatically when your subject breaks the path of an infrared beam projected out of the trigger box itself. This works equally well day or night.

Figure 2.17 Remote triggers. Left: breaking an invisible IR beam projected and refected across the path of some event. Centre: two IR beams angled to correspond to one point in space. Only an object breaking the beams here triggers the camera. Right: ultra-high-speed fash triggered by sound detection.

With high-speed analytical work, a sudden happening – a spark or one object striking another, for instance – can trigger events via a light or sound sensor or by breaking a strategically placed beam. Here you can set up the camera in a darkened studio with the shutter locked open and using the trigger to fire an ultra-short-duration fash. Most trigger units allow you to tune their level of sensitivity to suit ambient conditions, sound or light. You can also dial in a chosen delay (milliseconds or microseconds) between sensing and firing to capture the event a little after trigger activation.

Instant-picture (Polaroid) adaptors

Instant-picture adaptors for ‘self-developing’ film are made to ft most professional-type small-, medium- and large-format cameras, provided they have detachable backs. Peel-apart instant-picture material (page 265) is necessary, otherwise your result is laterally reversed. Small- and medium-format cameras only use film in pack form – two 35 mm pictures can be exposed side by side on one sheet if the back adaptor incorporates a slide-over device. Large-format cameras can use either packs or individual pull-apart sheets in envelopes, which push into a back inserted into the camera like a sheet film holder. Backs for instant-picture sheets also accept some regular sheet films in envelopes. This is useful if you do not want to keep changing from an instant-picture adaptor to film holders. Instant pictures are not only invaluable for previewing results and checking equipment, but your instant colour print will probably be good enough to scan direct into a digital system via a flatbed scanner (see also Chapter 7).

Programming and data backs

Most advanced small-format (and some medium-format) camera systems allow you to replace the regular camera back with a dedicated program or data back. The substitute back is considerably thicker and carries electronic keys and a battery compartment. It extends the camera’s electronic facilities in various ways. For instance, some backs for motor-driven cameras allow you to program autobracketing – a quick series of frames each shot at a different level of exposure such as half, one or two stops’ progression. The same back may also act as an ‘intervalometer’, so that you can trigger pictures at intervals of seconds, minutes or hours, and preset the total number of frames to be shot. Usually the inside face of the back carries a printing

Figure 2.18 Special view camera accessories. Left: time-saving sliding back arrangement. A, aperture-setting indicator. F, film holder, with darkslide facing camera already removed (see text). L, link holds bladed shutter open when focusing screen (S) and reflex hood (H) are aligned with lens. Right: TTL exposure-metering equipment. Probe (P) has a spot-reading tip (S) you can move to measure any chosen area on the lens side of the focusing screen. A, electronic bladed shutter which operates with all lenses. C, control unit for setting film speed, etc.

panel of low-intensity LEDs to expose characters and figures through the base of your film, alongside or just within each frame. (The diode brightens or dims by varying its pulse rate to suit the slow or fast ISO speed set for the film.) This feature allows you to program in date, time, frame number, etc., or the camera can automatically imprint the aperture and shutter settings it made for each picture. A good programming/data back is expensive but invaluable for various kinds of record photography, especially time-lapse and surveillance work. It frees you from tedious logging of notes.

Special view camera backs

One or two specialist back accessories are made for view cameras, principally 4 × 5 inches. They are mostly designed to make the camera quicker and more convenient to use. For example, a sliding back reduces the delay between composing and exposing. Simple rails allow you to rapidly exchange focusing screen for film holder (Figure 2.11) or digital back. Meanwhile, the shutter is closed and set en route by an electrical or mechanical link between the front and back of the camera. Working in reverse, the shutter locks open when you return the focusing screen.

Other replacement view camera backs accept a spot meter probe. This measures image light reaching the focusing screen from the lens and can program an electronic bladed shutter to give you aperture-priority exposure control. Other forms of exposure program are unsuitable for view camera photography because the subject itself and movements mostly determine what aperture you should set. Elaborate ‘add-on’ items for view cameras are manufactured in quite small numbers, which makes them expensive. Some more than double the cost of an outfit. So although extras make your camera quicker and more convenient to use, they may not be justified unless you use large-format equipment most of the time.

Avoiding camera failures

Even the finest cameras are basically just machines and their users only human, so mistakes do occur from time to time. Every photographer must have occasionally lost pictures at the camera stage. The important thing is to minimize risks by setting up safety routines you follow as second nature, especially checks before and during shooting. It should be impossible for you to completely ruin any assignment through some failure of camera handling. Here are some typical hazards and suggested precautions:

• Misuse of unfamiliar equipment. This is most easily done with rental cameras and lenses. Check anything complex and strange by exposing and processing a test film before using it on an important shoot.
• The preset aperture fails tostop down within the lens of your SLR camera when you take the picture, usually due to sticky blades or a broken spring. The result is various degrees of overexposure (unless you set widest aperture). Do a quick pre-check before loading film. Set a small aperture and slow shutter speed, then notice if the diaphragm stops down by looking through the back of the open camera and pressing the release.
• Your shutter fails to open, or close, or fully close. The result is no picture, or fogging and vast overexposure. Often the camera mechanism sounds abnormal, but check by looking through the back of the empty camera or make a trial exposure on instant-picture film.
• Using fash, you get no image (perhaps just faint results from existing light) or, with a focal plane shutter camera, your correctly exposed fash picture only extends over about one-half or one-quarter of the frame. These failures are due to mis-synchronization (for example, part frames result from using fast-peaking electronic fash with a focal plane shutter at too short a shutter speed). Be wary of any camera which has an old X/M (or X/FP) switch for change of synchronization. Electronic fash fired on these M or FP fashbulb settings goes off before the shutter opens - no matter what speed is selected or whether it is a lens or focal plane shutter type. This error happens easily on a camera with a hot shoe and a sync selection switch tucked away somewhere else on the body. Pre-check by pointing the fash and empty wide-aperture camera towards a white surface in a dimly lit area. Through the open back of the camera you should briefly see the full picture area as a white shape when the shutter fires.
• A run-down battery, making the camera meter erratic or non-active - this may also cause failure of the camera’s electronically timed shutter and other circuitry. Always check with the battery state button when preparing for a session. Carry a spare set of batteries too, and as further back-up include a separate hand-held exposure meter. There are clearly advantages in having a camera body which, in the event of battery failure, still allows you use of at least one (mechanically powered) shutter speed.
• Mechanical jam-up of an SLR camera. The whole unit locks solid, often with the mirror up. Some cameras offer you a reset lever or (medium formats) have some accessible screw you can turn with a small screwdriver to release the mechanism. The best precaution is to carry a spare body.
• Shooting on already exposed film. This is most likely on 35 mm, 70 mm and sheet film, as regular rollfilm winds up on to a new spool, its backing paper marked ‘exposed’. Adopt a rigorous safety routine. Exposed 35 mm film can always be bent over at the end or rewound completely into its cassette. Each sheet film holder darkslide must be reinserted with the black top facing outwards after exposure. Seal 70 mm cassettes and all cans of bulk film with labelled tape.
• 35 mm film not properly taken up when loading. Consequently, unknown to you, the film fails to wind on by one frame between exposures. Get into the habit of noticing, after shooting two or three frames, whether some rotation of the camera’s rewind knob (or equivalent tell-tales) proves that film is actually transported inside the camera. Cameras with autoload mechanisms rarely suffer from this problem.
• Out of focus due to coming too close with an autofocus camera. Practise and get used to recognizing nearest focusing distance from the way, say, a head reaches a particular size in the viewfinder. This is also the result of selection of an incorrect autofocus point in a multi-zone autofocus system. Again, practise quickly, adjusting the AF point.
• Soft focus, and sometimes upset of the camera’s whole electronic system, due to condensation on the lens and internal mechanism. If this happens on the internal glass surfaces of a direct viewfinder camera lens, its effects are hidden until you see the results. Avoid bringing very cold equipment into a warm, moist atmosphere unless it is wrapped up and allowed to reach ambient temperature slowly.
• Obstruction of part of the picture. The cause is usually in front of the lens (your finger, strap, lens hood or a filter holder too narrow for the lens’s angle of view, etc.), especially with a direct viewfinder camera. Alternatively, it might be between lens and film (part of a rollfilm sealing tab fallen into the camera, crumpled bellows in a view camera used with shift movements or an SLR with its mirror not fully raised). Always glance into the camera space behind the lens as you are loading film. Fitting a hood of correct diameter will reduce the risk of something getting in front of the lens.

Remember the value of having an instant-picture back, to allow you to confirm visually that lens and body are working correctly - plus checking lighting, exposure and composition - at any time during a shoot. Some professional photographers habitually expose one instant picture at the beginning and another at the end of every assignment, as insurance. It is also a good idea to carry another complete camera (a 35 mm SLR, for example) as emergency back-up.

Comparing digital and silver halide camera equipment

Advantages of digital are:

• You get an immediate visual check on results (for example, displayed on a large studio monitor screen).
• No film or lab costs, or liquid processing in darkrooms.
• Sensitivity can be altered via ISO speed setting to match a range of lighting conditions.
• Exposure can be checked using the histogram to ensure correct scene intensity/contrast and to prevent highlights being ‘blown out’.
• You can erase images, and reuse file storage, on the spot. ll Colour sensitivity is adjustable to suit the colour temperature of your lighting.
• Camera images can be transmitted elsewhere rapidly and wirelessly.
• Digital image files can feed direct into a designer’s layout computer – ideal for high-volume work for catalogues, etc.
• Extensive ability to alter/improve images post-shooting.
• Digital image files are theoretically permanent, if correctly archived. ll Silent operation.

Disadvantages of digital are:

• Much higher cost of equipment at larger formats; this includes powerful computing back-up with extensive file capacity (RAM) necessary for high-resolution work. The technology is continuing to develop, meaning that equipment may require frequent updating, another source of expense.
• There are a huge range of knowledge and skills required to keep up with changes in the imaging systems, to ensure that your methods match standard workflows within the industry and to maximize the potential of the equipment. This needs extra investment from you in terms of both time and money.
• Digital workflow is not simply restricted to capture, but requires an imaging chain consisting of other devices such as a monitor and printer.
• Correct colour reproduction of a digital image from input to output requires the understanding and implementation of colour management, which is a complex and still developing process.
• Silver halide film still offers excellent image resolution at low cost – roughly equivalent to 3 billion pixels for every square centimetre of emulsion. Also, colour prints, particularly in runs, work out much cheaper by traditional neg/ pos chemical methods.
• The limits to final acceptable image size are highly influenced by the number of pixels per inch the camera sensor codes within a file. So when planning a large final print, you must start with a camera delivering sufficient pixels.
• High-resolution systems based on scanning are limited to still-life subjects.
• Cameras with digital sensors, like computers, are adversely affected by heat (i.e. from tungsten lamps).