Exposing Animals

A reader in Istanbul asks how she can take photographs of black cats that show the texture and not just the outline of their fur. This is the perfect excuse for the first WedPhotBlog post about setting exposure. Like setting the aperture, this is a huge subject, but one that I can introduce briefly and I hope usefully. I’ll do the science bit first and then we’ll have a look at some black fur.

Both film and digital cameras work by collecting light onto a detector. Most of the time this detector—a piece of film or a sensor—is kept in complete darkness. When you press the shutter on your camera, light is allowed into it and onto the sensor. The light comes through the lens, via a precisely controlled size of opening, then, after a precisely controlled period of time, darkness returns. Usually all of this happens before you have released the pressure of your finger from the switch that triggered the process.

John Hedgecoe in his New Manual Of Photography compares exposing a light-sensitive surface to reflections from your subject with filling an empty tumbler. The amount of water in the tumbler depends on the size of the pipe carrying the water—the aperture—and the length of time water is allowed to flow from the pipe into the tumbler—the shutter speed.

In any given situation, if the camera shutter is left open for a long time, say one minute, then lots of light can flow in. If it is left open for a short time, say one-four-thousandth of a second, then far less light can flow in. If you turn a tap on for tool long a time the tumbler will overflow. Similarly if you expose your film/sensor to too much light your image will be over-exposed. If you turn on a tap for too short a time there won’t be enough water in the tumbler for a decent drink. Similarly, too little light leads to under-exposure. Slow film, say 100ASA, is like a tall tumbler—it takes a lot of light to “fill” it. Fast film , say 800ASA, is like a short tumbler. Helpfully, digital cameras usually use the same ASA system to describe different levels of sensor light sensitivity settings.

Just as they can now autofocus in an “intelligent” way, modern cameras are extremely good at judging exposure times automatically. There are, however, unusual situations that can fool them. If you have ever tried to photograph people, animals, or buildings against a snowy landscape you will understand. The built-in light meters in even the most sophisticated cameras aggregate the overall level of light in clever ways but this means that they can be fooled by the surrounding brightness of the snow into thinking that the subject you are interested in is bouncing more light through the lens than it actually is. As a result, for example, the features of any human face against this background will be obscure because the camera will open the shutter for too short a time to allow enough light to be reflected from that face to define its features.

You can get around this kind of problem in many ways, but the simplest two are as follows:

1. You can make sure your subject fills the frame of your picture, so the background plays less of a part in the camera’s exposure calculations
2. You can force your camera to base its exposure calculations on the part of the image you are interested in, for example the skin of your subject’s face.

(I’ll write about other approaches to setting difficult exposures—using a handheld meter, compensating manually, exposure bracketing—later.)

How do you get your camera to weight its exposure calculation towards your subject? As well as the “focus lock” button that you can use to force your camera to focus on a particular (usually not centred) part of the scene, many cameras have an “exposure lock” button. This is usually labelled “AEL” or “A-EL”. The way you use it is usually the same as the way you would use the focus lock: you centre the target of your interest in the viewfinder of your camera, press the button down, keep it held while you recompose the picture, and then open the shutter with the button still depressed.

Choosing the part of the scene to lock the exposure on is harder than choosing which part of the scene to focus on. You should aim to hit the button when your view is centred on an area whose brightness falls in the middle of the range of tones you are interested in discriminating in the final image.

If you were photographing the dog in this photograph, for example, you would find a part of its fur that was reflecting the sunlight so it wasn’t completely opaque, but not an area that was shining most glossily. You are interested in recording the range of tones on the animal’s body, not the range of tones in the background. Metering on a “greyish” area of the dog’s fur—I mean “grey” by reflection; this dog was the same black colour all over—would probably your best hope of achieving that. (I am deliberately oversimplifying here.)

To be honest, this wasn’t the only technique I applied to capture that the texture of the dog’s coat. I used fast (1600ASA), contrasty (Fujifilm NEOPAN), true black-and-white film. This stock exaggerates mid-range differences in reflected light, but, if correctly exposed, does so pleasingly. What you lose in truth you gain in beauty. I also shot the dog in fairly strong, angled sunlight. The intensity and slight tilt of the sun’s rays helped to throw the surface of the dog’s coat into relief.

Because this film is a little grainy and I wanted sharpness around the dog’s eyes, I chose too large an aperture and left more of the dog out of focus than perhaps was best for capturing the look of the whole animal, but this does have the advantage of “pushing the dog’s head out of the frame” into the viewer’s face. I could have chosen a smaller aperture setting and focused on the end of the dog’s nose.