Camera basics: shutter-speed, aperture and ISO · by Simon Mackie
Aperture
The next item we can change on the camera is aperture. The aperture is the hole through which the light passes through to reach the sensor or film. You can actually control the diameter of this hole on your camera. On old style cameras, there is an aperture ring that goes around the outside of the lens. Moving it around changes the diameter of the aperture. Aperture rings look something like this:
Even though you might not have an aperture ring on your modern lenses, your lens still has the diaphragm inside that allows it to open and close, and you’ll have controls on on your camera that will allow you to control that diaphragm. Here’s a lens with the aperture fully closed, so you can see the aperture blades:
And here it is fully open (you’ll commonly see this called wide open)
Going back to the aperture ring on my old camera, you’ll see that the numbers look a little strange
2 2.8 4 5.6 8 11 16 22
These numbers are called f-stops, and like the stops we saw before while looking at shutter speed, moving up or down a stop halves or doubles the light let into the camera (the reason that the numbers look strange is down to some tricky math). Even though your camera doesn’t have an aperture ring, you’ll find that you can still adjust the aperture of your camera to these same values (although, depending on your lens, you might only be able to go as low as f4 or 5.6)
One thing that is really important to realize about the f numbers is that the smaller the number is, the larger the aperture is. This can be a bit tricky to grasp at first! In the images of the leses above, when the lens was wide open, that was f/2, and when it was closed, it was at f/22.
So, for any given scene with a set amount of light, if you increase the aperture by one stop (thus doubling the amount of light entering the camera), you’ll need to put the shutter speed down by one stop (and thus halving the amount of light entering the camera).
Aperture priority mode
Similar to shutter speed priority, you can set your camera to aperture-priority mode (usually Av or A on your mode dial). This lets you select the aperture that you’d like to take your picture with, and the camera will select the correct shutter speed to make the correct exposure. I find that this is the mode I use most often. The reason for this is because changing the aperture can have quite a dramatic effect on your photos by changing the depth of field.
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