EXPOSURE IN BIRD PHOTOGRAPHY
It’s essential to know the selected method of exposure inside out and expose images correctly.
This chapter takes a closer look at exposure basics, and I will also talk about how I expose in different situations. Exposure is all about the amount of light that hits the sensor, which you can control by changing the size of the aperture or the exposure time, or both. For example, if you change the aperture from f/4.0 to f/5.6, or change the exposure time from 1/125 second to 1/250 second, you halve the amount of light that reaches the sensor. The smaller the aperture (which is indicated by a growing number), the greater the depth of field (range of sharpness). Where aperture has an impact on the depth of field, exposure time dictates, first and foremost, how well you can freeze movement in your image, and it also plays a role in preventing camera shake. As a guideline, when you are photographing with a handheld camera and a 500mm lens without a stabilizer, the exposure time should be at least 1/500 second to avoid the effects of camera shake in your image. The latest stabilizers let you stop down remarkably and set the exposure time at 1/125 second, for example, and still get sharp images. The light metering mode influences exposure as well.
Metering Light
DSLRs offer a range of light metering modes, which determine the region in the frame where the camera meters light and how it is weighted. Nikon and Canon have the following light metering options:
Spot: The camera obtains a meter reading from the center of the frame or a specific selected focusing point that is off center. You can use Automatic Exposure lock (AE lock) with this mode and reframe the image. If the meter is reading a spot that is either too dark or too light, the exposure can fail completely.
Center weighted: The camera uses the whole frame and weights the center of the viewfinder. This mode is especially good for photographing flying birds. You can use AE lock with this mode and reframe the image.
Evaluative/matrix: This metering method is called color matrix in Nikon cameras and through-the-lens (TTL) full-aperture metering in Canon cameras. This is the recommended setting for most situations, and it works well in bird photography.
When photographing flying birds, I suggest using center-weighted metering because it leads to a more accurate exposure than metering the entire frame. Also, you need to apply less exposure compensation—overexposure and underexposure—than evaluative/matrix metering. In some extreme lighting conditions, when the difference between light on the subject and light in the background is considerable, spot metering is justifiable. Nonetheless, I mostly use the evaluative/matrix metering modes. It might be easiest to learn one mode like the back of your hand—experience will teach you to judge how much you need to correct the exposure that the camera calculated for you in any given situation. If you want to momentarily change the mode in the middle of a session, you need to remember to change it back right away, or you will probably get some bad exposures.
An Osprey in full sunlight against a black background, which is difficult to expose correctly (Pandion haliaetus)
Nikon D3S, 500mm f/4.0, 1/2500 second, f/8.0, ISO 1600, continuous focus with 51 focusing points, Gitzo tripod, Manfrotto 501 video head. Kangasala, Finland, September 2010.
Checking the exposure is easy with a digital camera; you can check the brightness histogram on the LCD monitor immediately after taking the picture to see if the frame is exposed properly. It’s very important to get the exposure right, and preferably have the histogram reach all the way to the right edge because then you know you have the maximum amount of tonal values in the image. This is called exposing to the right (ETTR). Most cameras have a setting that makes the overexposed areas flash on the LCD monitor, and it marks them with a different color in the preview. State-of-the-art cameras tolerate some level of overexposure without undue data loss, but it’s smart to keep an eye on the histogram and tweak the exposure if the histogram seems to lean too heavily to the right edge. When it is skillfully applied, moderate overexposure can often be recommended because it allows the sensor to capture the maximum amount of information and therefore, particularly with high ISO values, it gives you the best results.
In September 2010 I was photographing Ospreys at the Osprey Foundation in Kangasala, Finland. It was early in the morning, the sun was shining on the white Osprey, and the background was in the shade. I used evaluative/matrix metering and manual exposure. Compared to the reading in my camera, I had to underexpose by more than two stops to avoid clipped highlights on the white parts of the bird. During the same photo trip, I captured a Lesser Black-backed Gull flying against dark water. To avoid overexposing the gull’s white head, I had to underexpose by one to two stops.
On another trip in April 2010 I was photographing Black-legged Kittiwakes on the Hornøya bird island in northeast Norway. They were set against a background that was in the shade. Here also, I had to underexpose more than two stops to make sure that their white heads wouldn’t be overexposed.
The white head of a Black-legged Kittiwake is easily overexposed when photographed against a dark background (Rissa tridactyla)
Nikon D3S, 500mm f/4.0 plus 1.4x extender, 1/2000 second, f/10.0, ISO 800, one-shot focus with one focusing point, Gitzo tripod, Manfrotto 501 video head. Hornøya, Norway, April 2010.
Exposure Modes
The photographer influences exposure by controlling the amount of light that hits the sensor. This is accomplished by changing either the aperture or the exposure time, or both. DSLRs allow manual adjustments of both the aperture and the exposure time. They also have preprogrammed exposure modes that let photographers control either the aperture or the shutter speed, while the camera controls the other one. You can also let your camera select both the aperture and the shutter speed.
More advanced DSLRs have exposure modes that are more or less suitable for bird photography:
P (programmed): The camera determines the shutter speed and the aperture for the best possible exposure, incorporating the focal length to minimize camera shake. This is relatively foolproof, but it is better suited to a family trip or a casual day out than photographing birds.
A/Av (aperture priority): You set the aperture, and the camera sets the shutter speed. This mode lets you control the depth of field. Setting the maximum aperture (smallest aperture number) that the lens allows gives you a shallow depth of field, which results in the fastest possible shutter speed. Many bird photographers use this mode.
S/Tv (shutter priority): You set the shutter speed, and the camera sets the aperture. This is good for freezing and blurring movement. Experience gives you the knowledge to assess which shutter speeds freeze different-sized birds in flight. For example, a crane’s wings are frozen at a mere 1/500 second, whereas a puffin requires a minimum of 1/1000 second.
M (manual): You set both the aperture and the shutter speed. This gives you maximum control. This mode can be a bit slower to use in the field, but is excellent in situations where the background behind a flying bird alternates between a lighter sky and a darker forest. I use this mode in Nikon cameras. Manual exposure compensation is also easy.
A Black Woodpecker flying against a blue sky (Dryocopus martius). A typical example of a situation that requires overexposure by one f-stop.
Canon EOS-1D Mark III, 500mm f/4.0 plus 1.4x extender, 1/2000 second, f/10.0, ISO 800, continuous focus with an extended central focusing point, handheld camera. Kuusamo, Finland, June 2009.
Exposure Compensation
Regardless of the metering mode, or the exposure mode, you can be faced with the need to either overexpose or underexpose against the metering result that your camera has calculated. It’s down to experience again; you will learn when to stop down and when to open up.
A typical situation for overexposure is when you’re photographing a bird flying in the sky. The lighter the sky, the more you need to open up. When you photograph against snow, you usually need to give more light to the sensor than what your camera meter says.
In situations where a light-colored bird is set against a very dark background, you may have to stop down the exposure compensation—sometimes a lot. Otherwise you risk overexposing your subject.
Some cameras let you set an automatic ISO mode, which means the camera will automatically raise the ISO sensitivity if there is not enough light for the exposure you set. This can be a useful feature with new camera sensors, which tolerate extremely high ISO values.
Safety shift is an automatic setting that either increases the exposure time or opens the aperture, until the exposure is correct, if there isn’t enough light for the aperture and shutter speed that you selected.
Bracketing
Your camera may have an option for automatic exposure bracketing. This means that your camera can automatically bracket exposures for multiple frames so they differ by 1/3 stop increments, for example. I try to always set the exposure as accurately as possible, but lately I have been experimenting with bracketing. Combining frames with different exposures by using the high dynamic range (HDR) technique can open new frontiers in bird photography.
It’s vital that you practice changing your camera settings so you can change the aperture, shutter speed, and ISO value, in particular, without having to raise your eye from the viewfinder. You need to be able to make the necessary adjustments by feel to avoid missing great opportunities. To a photographer, this is just as important as being able to drive without having to look at the pedals and gear shift!
Depending on the selected metering mode, a Cinereous Vulture against a white sky requires overexposure by zero to two f-stops (Aegypius monachus)
Canon EOS-1D Mark II N, 500mm f/4.0, 1/2000 second, f/5.6, ISO 400, continuous focus with an extended central focusing point, handheld camera. Mongolia, June 2007.