What is Aperture?

Getting to grips with camera aperture settings

Definition of Aperture

In general usage aperture just means an opening or gap. But what is the definition of aperture in photography?

Well you've probably heard it mentioned a lot because it is one of the key elements, over which you can have control, in producing a photograph.

The aperture is basically a hole in the lens which admits light into the camera. It's formed by a ring of metal blades called the iris or diaphragm, which can move to either expand or contract the aperture. So, as the size of the hole changes, more or less light enters the camera, affecting the exposure of an image.

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Exposure

The bigger the aperture, the brighter the photo will be, because more light is allowed on to the sensor. But shutter speed also affects the exposure, and the two things work reciprocally.

As light enters through the aperture, the shutter speed determines for how long it can pass into the camera (introductory article - what is shutter speed?).

The combined effect produces the exposure value for your image. It's really easy to get the hang of this system, which will give you a lot more creative control over the camera. But what is aperture measured by?

Camera aperture settings: F - stops

If shutter speed is shown in seconds and fractions of seconds, how do you quickly and easily recognize a given size setting for the aperture? It's just a sequence of numbers - simple! Each number corresponds to a size setting and is called an f - stop or f - number, because the number is preceded by the letter f.

The only thing to learn is that the smaller the number is, the larger the aperture is. So for example, f 2.8 is a really wide open aperture, whilst f 22 is very narrow. Each f stop is twice as large as the next smallest (higher number)and half the size of the next largest (lower number). Luckily for us, f numbers are a universal measurement and apply as such across all lenses.

Both the shutter speed and aperture settings that you choose influence the visual qualities of a picture beyond just the exposure. As far as the aperture is concerned, this involves the depth of field.

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Aperture and Depth of field

The depth of field of a photograph has a really big impact on the character of an image. Depth of field refers to the area of sharp focus, which extends a given amount behind and in front of the actual point you focus the camera on.

Sometimes, as with landscapes, you'll want a large depth of field, other times, often when shooting people, a small depth of field can intensify the subject.

How to use aperture to influence depth of field? Simple - The smaller the aperture, the greater the depth of field and vice versa.

I don't know how technically accurate this is, but I think of it as kind of like squinting! A big aperture takes in loads of light and flattens out the image, whilst a narrow aperture sort of squints to see deeper into the scene and pick up more detail.

Also, bear in mind that the closer you stand to your main point of focus, the shallower the potential depth of field becomes.

So that's it. Hope it helped. What is aperture? It's one half of the system, along with shutter speed, that allows you to control exposure, and it determines the depth of field.

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So now you've read this page on 'what is aperture', it's time to get to grips with shutter speed.

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