What The F-Stop! Understanding Aperture

Manual photography - so simple in principal, yet so damn brain bending when you think about it all at once. Let’s start with A, for Aperture…

Aperture

F-numbers are the unit used to indicate how much light is being let in.

The more open it is (which corresponds with a small f-number on your camera) the more light comes in.

The more closed it is (which corresponds with a large f-number) the less light is let in.

(Think about the way your own pupils work - on a bright day they will be small, whereas in the dark to help you see, your pupils dilate to let in more light)

A small f number = large opening = more light coming in
A large f number = a small opening = less light coming in

So far, so simple…

The aperture also influences the depth of field.
Depth of field is the area in front and behind the subject that is in focus.

A small f number (large opening) = a smaller area in focus
A large f number (small opening) = a larger area in focus

So, if you want everything in your image to be in focus, choose a large f number.
If you want to blur out the background in an image pick a small f number.

Another thing that influences depth of field is distance – the greater the distance between you and your subject, the greater the depth of field.

One more thing…

Light conditions - Aperture is linked to shutter speed!

Slower shutter speed (more light let in) = more time open = blurred subject
Fast shutter speed (less light let in) = less time open = frozen subject

Slower shutter speeds can compensate for when your aperture is letting less light in (because you want a larger area of your picture in focus)

Large f number (small opening) = larger area in focus but less light means could be under exposed.

Using a slow shutter speed will let more light in, but you risk a blurry image.
If you don’t want motion blur, you will have to either sacrifice how much of your picture is in focus or how bright your picture is.
Faster shutter speeds can compensate for when your aperture is letting a lot of light in (because you want a smaller area of your picture in focus)

Small f number (large opening) = smaller area in focus but too much light means it could be over exposed.

Using a faster shutter speed will let less light in, but it means you won’t be able to capture movement in your subject.
If you want to capture movement, you will either have to have more of your picture in focus (to make the aperture smaller) allowing you to have a slower shutter speed or risk having an over exposed image.

There are other factors involved, including film speed and lens type, but the aim here is to keep it simple. Once you start practicing, and can understand how aperture, depth of field and shutter speed interact with each other, you will have much more control over the outcome of your images!