What is Aperture in photography?

What is Aperture?

Aperture refers to the diameter of the opening in the lens. The larger the aperture the more light gets through to the sensor (or film in the old days); the smaller the aperture the less light. Basically I like to think of it as the hole that lets light through.

For example, the images below are of my trusty Nikkor 50mm 1.8 lens (Sorry about leaving my fingers in the shots, but I just thought it’d be good to see the aperture in action!)

@ f/22            @ f/8            @ f/2.8            @ f/1.8

How does Aperture work?

Aperture is expressed in F-Stops (so f/1.8, f/5.6 - f/8 - f/11, etc.). As you can see in the images above, it’s an inverse relationship between the F-Stop and the size of the hole. So the smaller the F-Stop, the larger the opening on the lens and viceversa. The 50mm lens pictured above has an aperture range of f/1.8 to f/22. So the fastest aperture (biggest hole) is f/1.8 and the slowest aperture (smallest hole) is f/22.

Photographers refer to the aperture of the lens in terms of speed (ie. fast lens/slow lens) because the smaller the F-Stop (big hole) the more light gets through, so the sensor needs less time to expose correctly. Therefore, a “faster lens” is one with a very wide minimum aperture. This is usually f/2.8 or smaller.

This takes a while to get at first, but it will quickly become something you don’t even think about and just “get”. In summary:

• A small F-Stop (like f/1.8) means the aperture is wide open (big hole) and will let more light through, therefore requiring a faster shutter speed.
• A large F-Stop (like f/22) means the aperture is closed down (small hole) and will let less light through, therefore requiring a slower shutter speed.

Faster lenses are usually much more expensive than their slower counterparts. For example, my 50mm f/1.8 costs around US$100, but the 50mm f/1.4 is about 4 times more expensive.

Why is Aperture important?

Because the aperture you choose will have a dramatic effect on the photograph. For example:

• A larger aperture allows you to:

1. Obtain shallow depth of field, which means that part of the image will be out-of-focus (portraits). The photographs of the lens above were shot with a relatively wide aperture, so the background came out blurred. It’s actually a brick wall.
2. Shoot using faster shutter speeds to freeze action (sports)
3. Shoot in low-light situations, by allowing a faster shutter speed.

• A smaller aperture allows you to:

1. Obtain large depth of field to keep everything in the image in focus (landscapes)
2. Shoot using lower shutter speeds to blur action (waterfalls)
3. Shoot in very strong light.

Comments

[Jules]

Great pictures to describe your point!
I'd love to use this tutorial to teach my photography students.
Thanks Again!
Jules

[Gabriel]

Hi Jules, thanks for the comment. And happy for you to use this for education purposes. The content on this site is licensed under Creative Commons, so feel free to use it. I just ask that you give credit and link back to it where appropriate.

Apologies for the late reply. I have comments turned off for new articles and hadn't been checking.

Link text