4

Exposure

Photography without light is like fishing without water—relatively pointless.

Light sources emit visible and invisible rays, and objects reflect a percentage of these rays back. A specially shaped piece of glass bundles parts of this light and projects an image onto grains of silver salts, triggering a chemical process that causes them to change and turn black in the exposed areas.

Without light, we would not be able to take photos. Light is technically necessary, but can also be used creatively. Light has direction, intensity, and color temperature. It can be emitted by a point or area source of light.

In school, you probably learned that you can mix the colors of light. The white sunlight consists of light of different wavelengths, and every monitor is composed of many small red, green, and blue pixels that can work together to represent almost any visible color. For the exposure, the intensity (and color) plays a very important role—particularly the intensity of image areas important to the photographer. Generally, it’s the subject in the picture that we want to expose correctly. With the digital camera, you can check the result directly on the display. That makes it much easier to correct exposure errors quickly and take a second shot.

It’s a whole different story if you are out shooting with a 1950s Voigtländer Bessa. The camera offers neither a preview nor a light meter, and you’ll need to feed it the right settings before it can give you a picture with the right exposure.

4.1Stops

In the world of photography, you often hear people talk about aperture stops, exposure values, f-numbers, f-stops, or just stops. All these terms mean basically the same thing, and refer to a relative unit for measuring the exposure. In brief: If someone says, “Expose one stop brighter!” or “Open up one stop!” it means, “Let in twice as much light!”

The term aperture stops refers to the aperture, but you can also change the exposure via the shutter speed, ISO, or with a combination of all three values.

Here are a few examples:

Aperture, shutter speed, and ISO value have a triangular relationship. It’s referred to as the exposure triangle.

For example, if you increase the shutter speed by one stop and simultaneously reduce the aperture by one stop, the exposure stays the same. But the smaller aperture changes the depth of field and the longer exposure changes how movement is represented in the picture.

4.2F-Numbers

The f-numbers with their strange fractions and odd notation are quite easy to understand and even easier to work out. Important for understanding the numbers, especially their inverse nature (bigger numbers mean smaller apertures), is knowing that their sequence describes a relationship between the focal length (f) and the size of the aperture opening.

Aperture ring Minolta 35mm F1.8

You can easily work out the f-numbers yourself by looking at every second number. Each of these numbers is double the previous, apart from a small rounding-down between 5.6 and 11.

So if you want the exposure to be two aperture stops brighter or darker, you simply need to double or half the aperture number. That’s a quick way of working out the f-numbers for an aperture stop.

4.3Light Metering

Before we get into the topic more deeply, it’s important to familiarize yourself with the two fundamentally different approaches to light metering: reflective metering and incident metering.

4.3.1Reflective Metering

With reflective metering, you are measuring the light reflected back towards the camera by the subject. This method is used by all cameras with integrated light meters. The aim of the light meter (exposure meter) is to get whatever is in front of the camera onto the film in such a way that the exposure is as much within the film’s contrast range as possible. That works best if you choose an exposure that gets the average light of the scene into the middle brightness range.

Reflective metering is not entirely without problems: in the same light, differently reflective subjects in front of the camera result in different light meter readings, so the light meter is initially a gray meter. The result is that a white wall will be depicted as gray, and so will a black curtain. This rather technical approach contradicts our creative view because we know that white walls are white and not gray. Instead of the white wall, imagine a black cat in a coal cellar. Again, the light meter will try to get the exposure right in technical terms, and again the exposure will end up in the medium gray range.

The light meter always tries to do its job: getting the exposure as perfect as possible and making the best use of the film’s contrast range. Modern light meters in digital cameras try to use integrated computer databases to recognize what’s in front of the camera and compensate accordingly. This is referred to as matrix metering or evaluative metering, but in the case of the black cat in the coal cellar, even these systems can’t cope.

So, your job is to not just blindly apply the results of the light metering, but to interpret them and adapt them accordingly before you transfer them to the analog camera. Then, you can decide to expose the picture of the cat in the cellar darker than the light meter is indicating. For a white cat in the snow, you would need to pick a lighter exposure than the light meter indicates.

4.3.2Incident Metering

While reflective metering gives different results from picture to picture depending on what you point the camera at, the results of incident metering are much more consistent. Incident metering only measures the intensity of the (incidental light) light that falls onto the subject. In this case, it’s completely irrelevant if the subject is black, white, or striped.

With incident metering, black subjects are depicted black in the photo, and white subjects are white. Everything is in its proper place in terms of exposure. But even incident metering is not entirely free of problems. To measure precisely, you need to be where the subject is. You can only get a good result if you are measuring in the same light that’s illuminating the subject. That may be fairly easy if you are shooting a portrait in the studio, but spontaneous snapshots are trickier. In landscape photography, for instance, you can’t just take your light meter and drive over to a far-off mountain to measure the light several miles away.

Incident metering with a modern light meter

The following sections will show you how to achieve good exposures in such situations.

4.4Without Light Meter

First, let’s make things easy. Before the light meter was invented, people still managed to take photos with good exposure. Photographers simply used figures based on their experience, or compensated for minor exposure errors later in the darkroom during processing or enlargement. These empirical values were then turned into a few rules of thumb that are still applicable today.

4.4.1Sunny 16

The Sunny 16 goes back to the time when cameras did not have light meters, but is still as valid today as it was 50 years ago.

The approach is simple. First, the camera needs to be in manual exposure mode (M).

1. 1. Load a film with an ISO value suitable for the lighting situation (ISO 100, for example, for sunny situations).
2. 2. Set the exposure time to the reciprocal value of the inserted film: so, for ISO 100, set it to 1/100 second; for ISO 400, set it to 1/400 second.

That’s all you need in terms of preparation. Now you just have to set the following aperture depending on the lighting conditions:

This rule works for both analog cameras and modern digital cameras.

Looney 11

The Looney 11 is based on the Sunny 16 and designed for shooting pictures of the moon. Such a special case throws any light meter, so this rule of thumb comes in handy.

Again, follow the same steps as before. Start by setting your camera to manual exposure mode (M).

1. 1. Load a film with an ISO value suitable for the lighting situation (ISO 400, for example, for night time).
2. 2. Set the exposure time to the reciprocal value of the inserted film: so, for ISO 400, set it to 1/400 second. For ISO 800, set it to 1/800 second.

That’s all you need in terms of preparation. Now you just have to set the aperture depending on the lighting situation to see the moon in all its beauty:

This rule works for both analog cameras and modern digital cameras.

4.5With Light Meter

Nowadays, we usually work with a light meter. You can either use the light meter inside your digital camera, or if you want to be a bit more hands-on, you have the following options:

4.5.1Handheld Light Meter

At flea markets, in camera exchanges, or online, you will often find secondhand light meters. With a few exceptions, they work fine.

Without Battery

For a while, selenium was used as light-sensitive material in light meters. This material creates electricity from light, which made it ideal for light meters that worked without batteries. Sadly, many secondhand selenium light meters are only good for the museum these days, because selenium ages over time and loses its properties, especially if it’s constantly exposed to light and has not been stored in a dark drawer.

So beware—especially if the light-meter reading differs significantly from your digital camera’s reading.

Sixtomat light meter with selenium cell

Battery-Powered

The prime example of a used, battery- powered handheld light meter that still works very well today is the Lunasix 3 (known as Luna Pro S in the USA) by Gossen in Germany. Millions of these meters have been sold since 1966.

The electronics of the Lunasix 3/Luna Pro S are designed to be used with mercury batteries, which may be hard to find today. Gossen offers a battery adapter, so you can use two silver oxide batteries instead (type Varta V 76 PX or Duracell D 357 H). The adapter takes care of battery size and also contains a diode for the correct battery voltage.

Caution: Light meters from the time of orthochromatic film (generally pre-1950) do not measure red light because the film was not sensitive to red light. These meters are only suitable to a limited extent, including light metering for modern black-and-white film.

Light meter Gossen Lunasix 3

4.5.2Smartphone

If you don’t want to cart around yet another gadget, you may find you already have a light meter in your pocket. Any current smartphone with camera can be used for light metering. You can get suitable apps in the relevant marketplaces and app stores.

As an example, let’s take a look at the Pocket Light Meter app for the iPhone. It works pretty much like many other light metering apps:

1. 1. Select two of the three exposure parameters—in this example, aperture 8 and ISO 100.
2. 2. Aim the camera at the scene you want to expose.
3. 3. Read the third parameter (here, 1/250 second shutter speed) and transfer the value to your camera.

For Android, we have had recommendations for the Light Meter Tools and Lightmeter apps.

4.5.3Digicam & Gray Card

If you have an 18% gray card, you can use it for white balance as well as for light metering. The reflectivity of the card is calibrated to 18%, which is also the value the light meter is set to.

Again, the procedure is easy:

1. 1. Place the gray card directly in front of or next to the subject.
2. 2. Measure with the light meter directly off the gray card. Make sure you are as close as possible without letting your own shadow fall onto the gray card. The card should fill the picture frame.
3. 3. Set the camera to the measured values.

Pocket light meter for an iPhone

4.5.4Professional Light Meter

In the professional league—particularly for studio work—photographers use light meters that can deal with normal (continuous) incident metering, reflective metering, and also metering for flash units. The measured values can be stored in the memory to determine average exposures from multiple readings. With interchangeable domes, some light meters can be converted to highly accurate spot meters. The price for such a device is usually several hundred dollars.

Sekonic L-358

4.6Light Metering with the Zone System

The Zone System is not just about the creative aspect of film photography, but also the chemical, technical, and economic aspects. If you deal with film photography, you will come across the Zone System sooner or later. Be warned: there is a lot of voodoo floating around the Internet regarding the Zone System, and it causes confusion among newbies. In this chapter, we will use some examples to show you how easy working with the Zone System can actually be.

The Zone System was developed by the U.S. photographers Ansel Adams and Fred Archer. It is designed to get the contrast of the subject in the picture (taken in analog large format) as comprehensive as possible in the finished positive image, from exposing the negative to processing the film and enlarging the photo. Particularly in large format, experiments and failed shots have always been expensive and time consuming. By creating a system for this process, photography results become more predictable, and the amount of work and cost involved in the process was reduced. Parts of the Zone System can also be applied to smaller formats.

Simplified Zone System

Describing the details of the Zone System would go way beyond the scope of this book, but we want to take a closer look at the first part, so it’s usable for other formats, as well. It’s all about the right exposure of the picture. With film photography in particular, getting the exposure right is important because you can’t just take a quick look at the histogram, adjust, and take a second shot to correct. The Zone System is an important tool that makes it extremely easy to get the exposure right where you want it to be.

Let’s clear up a frequent misunderstanding: the zones in the Zone System do not refer to spatial areas in the picture, but brightness levels. The Zone System divides the subject contrast of the scene you are shooting into 11 zones numbered with Roman numerals. Zone 0 is pure black, zone X is pure white. In between, you have different brightness levels. Each zone corresponds to one aperture stop difference in exposure.

The middle of the range is defined as zone V, and represents medium brightness. Light meters are set to zone V. For example: in diffuse light, if you point your light meter at an evenly lit white wall and then expose the picture with the settings shown by the light meter, your negative will render the area with medium brightness in zone V.

If you now measure an 18% gray card instead of the white wall and shoot it, it will be exposed correctly in zone V; but the white wall will be too dark. That’s where the Zone System can help us. As soon as you’re comfortable with which zone makes certains subjects looks best, you can get the exposure for correct straight away without having to experiment.

The 11 zones of the Zone System

Examples

Using this table, let’s take another look at that white wall. We now know that our light meter feels drawn to zone V. But the white wall wants to be in zone VII, so it needs to be exposed two stops higher. Let’s assume our light-meter reading of the white wall resulted in the following exposure: ISO 100, f/8, 1/400 second.

Now all we need to do is correct this exposure two stops upward compared to the measurement. For the correction, we could theoretically use any of the three parameters (ISO, aperture, or shutter speed). But since we put a film with ISO 100 into the camera and aperture 8 offers the desired depth of field, adjust the shutter speed two whole stops upward. So we double the time twice: ISO 100, f/8, 1/100 second. The photo we expose now puts the white wall into zone VII.

Let’s work through another example: we are sitting in the audience and want to shoot a photo of a concert on stage. The musicians are lit brightly, and the big black curtain behind the stage shows a bit of detail, but is mostly black. The light meter looks at the whole scene, the black curtain is large compared to the lit musicians. The light meter determines the following exposure: ISO 800, f/4, 1/50 second. Again, the light meter has tricked us, and will expose the black curtain as zone V, i.e., as middle gray. So the musicians will be hopelessly overexposed.

The table shows that the black curtain will have detail somewhere between Zone II and III. So we correct the exposure downwards, this time via the aperture. Instead of f/4, we use f/8: ISO 800, f/8, 1/50 second. The curtain will now be correctly exposed.

The Gray Card as Reference

What to do if there are neither white walls nor black curtains for you to use as reference for light metering? You can bring along your own reference in the form of an 18% gray card (available in photo retail stores). This gray card is already in zone V, which makes life easier for you. Hold the gray card into the same light as the subject for which you want to find the right exposure. The values determined via spot metering (or close-up metering with the normal light meter) can be transfered directly to the camera.

A white wall with an additional light source in the picture is a challenge for finding the right exposure. This issue is solved here via spot metering on the light source, and shifting the brightest areas to zone VIII. The wall then automatically falls in between zones VI and V.

Your Palm as Reference

We also carry another exposure reference point around with us all the time: the palm of our hand. Even in summer, it will never change in reflectivity. As long as we know which zone our palm is in, we can use it for light metering.

You simply have to work out just once what zone your palm is in. The easiest way is with a digital camera in exposure mode (M). First, set the camera’s light meter to a diffusely lit gray card in such a way that the measurement is in the middle. Now, hold the palm of your hand into the light you’re exposing for, and look at the scale of the light meter. Many fair-skinned peoples’ palms are in zone VI, i.e., one aperture stop over the middle.

This is how you now measure the exposure:

1. 1. Hold your palm into the same light that the subject is in.
2. 2. Set the exposure so the light meter is one stop above the middle when measuring your palm.
3. 3. Transfer the values to the camera.

Done.