Arnoud Quanjer Wildlife Photography

In this article, I’ll introduce you to the basic elements that you can use to control exposure in your shooting. If you have a digital SLR, there will be a way to set all of these controls on your camera, but since they differ between manufacturers and models, you’ll need to refer to your camera’s manual to find out exactly how to change them.

All cameras, whether an ancient film camera, or a more modern digital, work in pretty much the same way. Photographs are taken by letting light fall onto a light-sensitive medium, which records the image. Traditionally, this has been film, but nowadays it's usually a digital sensor. The more light that falls onto the film or sensor, the lighter the image. Put simply, a camera consists of a light-tight box that stores a light-sensitive device (either a film or a digital sensor), a lens that magnifies and focuses the image onto that light-sensitive device through a hole in the box (called the aperture) , and a shutter that opens and closes when you press the shutter release, exposing the film or sensor to the light; this is why a picture is sometimes called an exposure.

The amount of light entering the camera depends on the amount of light in the scenes that you’re photographing. A bright sunny cloudless day has more available light than a cloudy one, which in turn has more light than an indoor scene lit by tungsten lighting. To make the picture look right, we have to expose the film or sensor to the right amount of light. Too short, and the image will be dark, or underexposed. 

With most cameras, except basic “point n shoots” you have three variables that you can control:

• Shutter speed
• ISO
• Aperture

Aperture

You use the aperture for controlling the depth of field (DOF). In layman's terms this means that with the aperture you can define what portion of the picture will be in focus and what portion will be out-of-focus. The aperture works in f-stops. On your lens or camera body you will be able to set for instance f/5.6 or f/11. The minimum and maximum aperture depend on your lens. If you set a large f-stop like f/2.8 then you will only have a very limited DOF. When you set a small f-stop you will have a very broad DOF. When you are photographing a landscape you usually set a small f-stop like f/16 or f/22 because then almost the complete picture will be in focus. When you are making a portrait shot you would want to set a large f-stop like f/2.8. Using a large f-stop you get a very limited DOF and the background will be blurred. This sounds simple, large DOF = small aperture and limited DOF = large aperture. While this is true there is a catch to all this. Setting the aperture from f/2.8 to f/4 will halve the light that will reach the film. This means that if you would have a shutter speed of 1/250sec. at f/2.8 then to get the same exposure at f/4 you would have to set the shutter speed to 1/125 sec. Knowing what aperture to set takes practice. Some camera's will have the option of a DOF preview. What this preview does is close the aperture of the lens to the aperture you've set on the camera. This will enable you to judge the DOF through the viewfinder. This sounds great but it has its limitations. Because the aperture is closed down the amount of light that the lens will let in is less. This makes the viewfinder darker and that makes it more difficult to judge the DOF.

Shutter speed

With the shutter speed you control the amount of light that will reach the film. I usually set my camera to Aperture Priority mode (Av) and select the aperture manually and let the camera figure out the shutter speed that is needed to get a correct exposure. This can mean that the shutter speed becomes so slow that the camera has to be mounted on a tripod to avoid camera shake. If you for instance want to make a landscape picture at f/22 late in the day then you would probably get such a slow shutter speed that you can't possibly handhold the camera without introducing camera shake. To avoid having to use a tripod you could also select a wider aperture, but that would cost you the DOF which you need in a landscape shot. If you're using a digital camera you have the option of selecting a larger ISO value to get faster shutter speeds. If you're using a digital camera then rather use the ISO value to get faster shutter speeds than sacrificing DOF for faster shutter speeds. For handholding a camera the rule of thumb is that you can take a sharp picture while handhold the camera up to 1/focal length. This means that if you are shooting with a 300mm lens you could handhold up to 1/300 sec. Anything slower than this would require you to use a camera support such as a tripod or beanbag. If you use a lens with an image stabilizer then you can handhold up to two stops slower which means you could handhold a 300mm up to 1/75 sec.

ISO

The ISO of your film or sensor is a measure of how sensitive it is to light. “Normal” ISO, for taking shots outdoors on bright sunny days is 100. If you’re shooting indoors, or you’re shooting, say, sports and you want to use a high shutter speed, you may need to use a higher ISO (400 is common for sports photography). ISO goes in a doubling scale too: 50, 100, 200, 400, 800, 1600, 3200. Again, each increment relates to a doubling or halving of the sensitivity to light, so also equals one stop.

On modern digital SLRs you can often increase the ISO to 1600 or even 3200. The unfortunate trade off is that using a higher ISO introduces noise (on digital cameras) or grain (when using film). Noise or grain is usually unwanted. I say usually because some traditional black and white photographers use grain for creative effect – I quite like the image above. On modern digital SLRs, noise usually only becomes a problem at higher ISOs such as 800 and above, but it varies from camera to camera.

One of the real advantages of digital cameras is that you can change ISO on the fly – you don’t have to rewind the film and put a new one in if shooting conditions change, which is very convenient.