Exploring Aperture
Time for a quick look at another DSLR concept that confused me when I started out: aperture.
Your camera’s lens is there to focus light onto the sensor. Light enters the front of the lens and exits the rear… simple. But the lens opening is only a certain size, and this opening is referred to as the aperture. Try making a ring with your finger and thumb and imagine that this is your lens; the hole that you look through is the aperture.
The aperture controls the amount of light passing through the lens, just as the contractions and expansions of your pupil do in your eye. If you have a fixed aperture lens you can’t change the size of the hole, but a lens with a changeable aperture can be handy if you’re taking long-exposure shots and don’t want the image to over-expose (you’d set a small aperture) or if you’re taking photos in low light and don’t want the exposure time to be too long (you’d set a wide aperture in this case).
Aperture size also has another effect, though, in that it determines the depth of field. The depth of field is the range of distances within which objects will be in focus. A narrow depth of field means that you have to be pretty spot on with your focus since objects that are closer or further away will fall out of focus quickly, whilst a wide depth of field means much more will be in focus. A wide aperture gives a narrow depth of field, and a narrow aperture gives a wide depth of field as the light passing through the lens is pretty tightly focused by trying to pass through a narrow hole, a bit like pinhole photography. This is great if you want to play around with which objects are in focus and which aren’t, say if you wanted the background of an image to be way out of focus whilst keeping the main subject sharp.
OK, so that’s what the aperture is and some of what you can use it for, but how do you control it? If your camera’s on an automatic programme it’ll take care of itself, but choose aperture priority mode (Av on my Canon EOS 1000D) and you have control. The thing to remember is that aperture is measured in f-numbers and that the higher the f-number is, the smaller the aperture is. So the smallest aperture on my kit lens is f29, whilst the largest is f4.5. It seems kind of counter-intuitive, but it’s just one of those things you’ll have to get used to!
If you look at the image on this page you can see the aperture in the middle of the lens, a kind of iris made up of overlapping blades. You can also have a look at the aperture on your own lens by setting your camera to aperture priority mode, selecting a small aperture (high f-number), and pressing the aperture preview button. Have a look in the front of your lens and you should see it… if you’re not sure try pressing and releasing the aperture preview a few times and see if you can see it moving. And have fun experimenting with aperture sizes in your photography!
If you have any questions, comments, or I missed something, please feel free to chip in by leaving a comment.
If you enjoyed reading this why not buy me a coffee?