Learning about Aperture settings on your lens (part 1)

Aperture tends to be my favorite setting to control when I photograph.   In fact I'll often set my camera on aperture priority mode (we'll talk about shooting modes later.)  There are a few key questions I'll answer during this post:

What is aperture?

What do those strange settings mean: f/4, f/5.6, f/11?

What is depth of field?

Aperture is the opening in the lens that light travels through before it can reach your sensor.   Keep in mind it is not the lens elements themselves, but rather a mechanism within the lens that can open wider or close down smaller to control the amount of light that passes through.   Think of aperture like a water faucet.   The more you open it up, the more water passes through.    As you shut down or close the faucet, less water is allowed to pass through.


When you bought that DSLR it probably came with a lens or two.  Most of us start out buying a kit; camera body, lens, and accessories.   On your lens you'll see a few numbers listed on it, for example:

AF-S Nikkor 55-200mm 1:4-5.6

The numbers I want to discuss here are  4 - 5.6.    These numbers are related to the maximum aperture value of the lens.  Still confused?  Don't worry, so was I.    Note that when you discuss aperture values, you don't just use 4 or 5.6, you use f/4 and f/5.6.   This comes from a mathematical equation, but to keep in somewhat simple, we'll ignore the math (there will be plenty of that to come) and just remember that f/XX refers to aperture.

Aperture values are a series of numbers that are tied to the size of the opening.   To add to the potential confusion, they run opposite of what you might expect.    A smaller number like f/4 represents a larger opening than a larger number like f/8.

There is a standard list of aperture values that you'll want to become familiar with:

f/1.4  f/1.8  f/2.8  f/4.0  f/5.6  f/8.0  f/11  f/16  f/22

Values can go lower and higher than this range, but for now we'll just focus on these.

(here comes some math)

As we move up the scale, each increase in value represents a decrease in the opening by 50% (half the light will be allowed to pass through.)   As we move down the scale, the opening doubles (twice the light will be allowed to pass through.)  So....

aperture setting f/4 allows twice as much light through as f/5.6

OR  aperture setting f/5.6 lets in half the light as f/4.0

Let's look at a bigger jump:

aperture value of f/4 allows 4 times as much light through as f/8

OR aperture setting f/8 lets in 1/4 as much light as f/4  (Crazy!)