What is aperture in photography?

January 12, 2023

This is part of a series of articles dealing with the fundamental technical aspects of using a DSLR or mirrorless camera.

If you’ve recently purchased or been gifted a new interchangeable lens camera (whether that be a mirrorless or a digital single-lens reflex (DSLR) camera), and you’re completely new to photography – one of many things you’re probably getting your head around is Aperture.

Aperture, alongside Shutter Speed and ISO – we’ll deal with these in future articles – forms one side of the exposure triangle. That being, it’s one of the three settings you can use to control the exposure of an image. For the most part, these settings are set on the camera using the appropriate dial.

Aperture is represented by the f-number. If you look at the side of your lens, you’ll see a few numbers. One of those numbers may be expressed in the format, for example, of 4.0, or 3.5-5.6. This represents the maximum Aperture the lens will support when attached to your camera.

In the case of the image of the lens above, the maximum Aperture it supports is f1.8.

On your camera view screen, the Aperture setting will also be represented by fx.x.

Basically, the Aperture is the hole that allows light through the lens, with the f-number representing the size of this hole. The smaller the f-number, the larger the hole that allows light through the lens, which means a brighter image. A bigger f-number means a smaller hole.

Aperture stops

In photography, you’ll probably come across the term ‘stopping up’ and ‘stopping down’.

Put simply, stopping down refers to increasing the f-number. A ‘stop’ is doubling or halving the exposure. With aperture, the stops are as follows:

Aperture stops. Aperture stops go from 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, 32, with each stop up representing a doubling of exposure, and stop down representing a halving of exposure.

For example, stopping down from f2.8 to f4 means that at f4, half the light is going through your lens relative to f2.8. On the contrary, stopping up from f8 to f5.6 means that at f5.6, you’re doubling the amount of light going through your lens relative to f8.

Depth of field

Not only does Aperture control the amount of light filtering through your lens, it also controls depth of field of your image.

An image with a shallow depth of field will have a blurry, or out of focus, background with the subject being in focus. As seen in the image below. The out of focus area may also be referred to as bokéh.

A small f-number will result in a shallow depth of field. A large f-number will result in the whole image being in focus.

As such, although lighting conditions should be one factor as to how you adjust Aperture – you also need to consider what it is you’re photographing.

An image where there’s a main subject as the focus, such as a portrait of a person or an animal,  for example, should have a background that is out of focus. Therefore, regardless of the lighting conditions, the f-number should be as small as possible.

On the contrary, a landscape photograph should be in focus across the whole image – which is where a bigger f-number (smaller Aperture) ‘may be’ (there are ways around this, which we’ll go through in future articles) desirable.

That’s the basics of Aperture when it comes to photography. In the coming weeks, we’ll look at other settings and how they work.

Matt Hrkac

Matt Hrkac is a photographer and photojournalist based in Geelong and works across Melbourne and throughout Victoria.



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