Posted by Claire Wade
What is it?
The aperture is the size (diameter) of the opening of the lens. This hole is made bigger or smaller by small blades inside your lens moving in and out. The diagram shows some examples of different aperture sizes.
Think of it like your eye: when it is dark, your pupils (aperture) grow large to get more light in so that you can see; when the light is bright, your pupil tighten to pinholes to block out excess light.
So a big aperture is like a big hole in your lens that lets in lots of light. A small aperture is a small hole that lets in less light.
Aperture is measured in F stops, and confusingly the smaller the number, the bigger the hole. So, for example, f2.8 is a really wide aperture and f22 is a really small aperture.
So how is it useful?
Different sizes of aperture give varying results in you photography.
A wide aperture, such as f5.6 will give you shallow depth of field. Shallow depth of field means that only a small area of your photo is in focus. The rest of it becomes more blurred the further away it is from the focal point.
This is really helpful if you would like certain areas of your photo to stand out. For example, if you take a photo of a person in front of a busy background, with a shallow depth of field you can keep your subject (the person) in focus, whilst the background blurs out.
The image of Bod (my lovely cat) on the right was taken with an aperture of f4.5. This way, the cat’s face is nice and sharp, but the cluttered background is blurred. If the background was sharp, your eyes would get distracted from the cat, which is the subject of the photo. (It would be better to have no clutter at all in the background, but this cat doesn’t let me choose where she poses!)
A narrow aperture, such as f22 will keep most of the photograph in focus. This is useful when shooting a landscape and you would like the foreground and background all in focus.
The photo below with the yellow flowers in the foreground was taken with an aperture of f8. This kept the flowers in focus, but blurred out the buildings in the background.
The image of the Grand Canyon at the bottom of this article was taken using an aperture of f22. This means that most of it is sharp. The sun had just risen when this was taken so there was not much light and because of this, the shutter speed is 1/13 second. This is a bit too slow to avoid camera shake, so a tripod was needed.
So how do you use it?
It’s best to use Aperture Priority mode on your camera (on a Nikon this is marked as an A and on a Canon it is AP, other cameras may differ, but they should let you know in the manual). When in Aperture Priority mode, the camera will automatically set the shutter speed for you.
Aperture and shutter speed directly affect each other. To get a nicely exposed image, you need the correct amount of light to hit the camera sensor.
If the aperture is small, you need to let the light in for a longer amount of time, so that there is enough light for a good exposure.
If the aperture is wide, the hole is bigger, so more light gets in during a shorter amount of time. So you need a quick shutter speed.
A good way to understand this is to think of a full bowl of water. The full bowl of water is like having the correct amount of light for a perfectly exposed photograph. If the tap is only slightly open (narrow aperture) you need to leave the tap on longer (slow shutter speed) to fill the bowl. But if the tap is open fully (wide aperture), you only need it to run a short amount of time (fast shutter speed) to get the same amount of water to fill the bowl.
The best way to understand aperture is to try it out, the following exercise may help:
Set your camera to Aperture Priority. Find a static object, such as a bench and focus on it. Take three photographs. The first photo, set the aperture at f5.6, the second photo take at f11 and take the third at f22. Compare the difference. The first photo should have a blurred background, the third photo should be fairly sharp all the way through, and the middle photo will be somewhere in between.
If you find that all of your photos are blurry, it may be due to camera shake – especially if you shutter speeds are slower than 1/30 second. If this is the case, put your camera on a firm surface or use a tripod.