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Understanding Aperture
Article by Stephen Oachs

What is Aperture? What is Depth of Field?

Let's see if we can answer this with a little explanation and the interactive aperture demo below.

Before we get started on the details of how to control aperture, it is first important to understand what aperture is. Aperture is defined as, "a hole or an opening through which light is admitted." In your camera lens, as the diaphragm opens and closes, it allows more/less light into your camera, very much in the same way the pupil of your eye opens and closes to control the amount of light allowed in.

The graphic below, on the left, illustrates the inside of a camera lens and how it changes in size as the aperture (also know as f-stop) is adjusted. The lower the number, the wider the aperture is opened and the more light that is allowed in. This also has a direct effect on depth of field (DOF), which is the amount of depth in the scene that is in focus. A low f-stop (f/5.6 or lower) creates a wide DOF.

By sliding the red control from left to right, you can see how the aperture iris contracts, reducing the amount of light and DOF and brings distant areas of the scene into focus.


(Understand that this is a very simple approach to explaining aperture and there are many other aspects to how aperture controls DOF and that every camera lens has a different f/stop range. For illustration purposes we choose f/4.0 to f/16 but many camera lenses go lower than f/4.0 and much higher than f/16.)

Reader Comments

Angie - (August 12th, 2010 (3:32pm) PDT)
An easy to understand intro to the subject, thank you. I enjoyed the visuals especially.
Angel - (August 18th, 2010 (6:52am) PDT)
Great visual..very helpful. Thanks!
Morris - (September 20th, 2010 (2:09pm) PDT)
Can you clarify one thing for me? You say "A low f-stop (f/5.6 or lower) creates a wide DOF." Yet when I move the slider toward the low end of the f-stop spectrum, the depth of field seems to narrow (only the bear is in focus). When I move it to the high end (f/16) the depth of field widens and everything is in focus. So is the quoted sentence wrong, or am I missing something? Thanks.
Nathaniel Kidd - (December 14th, 2010 (6:51am) PST)
Thanks for touching on aperture a little bit, it is something that I struggle with, figuring out which numbers I want to use on a photo. Thanks!
Jeremy Hearne - (February 28th, 2011 (9:47pm) PST)
The interactive slider did not work on my computer....do you know why???
Tammy - (September 24th, 2011 (10:10pm) PDT)
Slider does not work.
Paul Harrus - (October 25th, 2011 (8:43am) PDT)
Looks very helpful but demo does not work on Firefox7/Mac. Please debug.
Arnie - (April 30th, 2012 (9:38pm) PDT)
If I want to control my aperture and get fast shutter speed should I use highter ISO to get the speed?? or do I have to use my TV setting.

Thank You Arnie
Michelle Pappas - (July 27th, 2012 (3:45pm) PDT)
This "tip" is so simple ....yet EXTREMELY helpful! visuals are awesome for learning....Thanks so much! You ALL ROCK!
charles leikam - (August 12th, 2012 (4:13pm) PDT)
i am just starting out using cameras,this really help me out to understand depth of field,i got some old photography books at the thrift store, reading them,do you have other things that i can read, example how shutter speed and iso and aperture all work toghter,thanks charles
Pukhraj - (February 28th, 2013 (2:19am) PST)
Awesome but the slider didn't work.


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