What Is Aperture?

The Pupil of Your Lens

I get asked "what is aperture?" an awful lot.

It's not that aperture is itself a particularily confusing topic, there are just a few common misconceptions that need to be cleared up.

It's NOT a feature of your camera
A larger aperture number is NOT a wider aperture

Phew! I'm glad we got that all cleared up! But I still haven't really answered the question have I?

So what is aperture?

Aperture indicates how wide your lens is open and how much light it lets it.

But there's a bit more to it than that.

Camera or Lens?

There's a good reason why aperture has become more confusing with the introduction of digital SLR cameras. With all modern digital SLRs, you change the aperture setting using the CAMERA.

But aperture is a feature of your LENS, not the camera. With older lenses, you change the aperture by turning a ring on the lens itself - this makes sense: if you want to open or close the aperture of the lens, you should change that setting on the lens right?

As digital SLR cameras evolved, the manufacturers realized it was easier to create an electronic bridge between the lens and the camera so that you no longer had to turn that lens ring to set the aperture. Now you can change it as much as you want just using the camera.

Important Point #1: aperture is a feature of your lens, not your camera.

The Aperture/Eyeball Relationship

You now know that aperture is a feature of your lens, and that it's an indication of how wide your lens is open.

Think of the aperture of your lens like the pupils in your eyes. When it's very bright outside your pupils narrow (or contract) to let less light into your eyes. When it's dark, your pupils widen (or expand) to let in more light so that you don't bang into furniture when you get up in the middle of the night.

Aperture is the same way, only it happens instantaneously AND it's under your control.

Let's say you're outside in your backyard taking photos on a bright sunny day. You'll be using a narrow aperture because there is plenty of light. You step inside for a moment and decide to take some photos in your dim living room. Now you have to widen the aperture since there is not as much available light.

Important Point #2: you can manually widen or narrow the aperture to let in more or less light.

But Wait...It's Backwards!

We now arrive at what is - without a doubt - the one thing that always complicates the answer to the "what is aperture?" question.

Important Point #3: the aperture number on your camera is INVERSELY related to the width of the aperture.

SMALL aperture number = WIDE opening = Lots of light
LARGE aperture number = NARROW opening = Minimal light

This is the one point that consistently drives new photographers to distraction. It's counter-intuitive, so let's run through some quick aperture number examples:

Aperture	Description
2.8	A very wide aperture that lets in a lot of light
8	A middle-of-the-road aperture that lets in moderate light
22	A narrow aperture that lets in very little light

See what's happening here? As the number gets bigger, the opening gets narrower.

Don't worry if this doesn't sink in immediately. It will take some time - the best way to understand this is to change your aperture setting often, and see what results you come up with.