Let’s Talk Photography, Part 5: Aperture

Note: This post was originally published by Mary Coleman on her blog “Simply Horse Crazy” on November 13th, 2013. She also took many of the photos featured, except where credited otherwise. Huge thanks to Mary for letting us repost the series here!

Finally we get to the last of The Big Three (but not the end of this series, mind you). Big Three, you ask? Well, let me explain…

“The Exposure Triangle”
We first talked about Shutter Speed, or the amount of time the camera’s shutter remains open and exposes the sensor to light. Then we talked about ISO, or the camera sensor’s sensitivity to light. Now we are going to talk about Aperture in this post. Together, the balance of these three things is the foundation for getting correctly exposed photographs…and really just good photography in general.

What is Aperture?

Imagine you’re in pitch-black room without any light whatsoever. You carve a tiny hole in one of the walls, and suddenly a little stream of light from outside enters the room. Then you decide to make the hole a little bigger, so more light enters the room. You keep making the hole bigger and bigger until the hole is really big and the room in really bright.

This is the basic idea of aperture–the size of the hole that lets light into the camera. Shutter speed may control how long light is allowed to reach the sensor, but aperture controls how much light reaches the sensor. Let’s look at the two diagrams below…ignore the numbers for now because I haven’t gotten there yet. You can clearly see that your lens can open really wide or it can really have a tiny opening.

The bigger the opening, the more light that gets in.

The smaller the opening, the less light that gets in.

Makes sense, right?

What’s With The Numbers?

Those are what us photography people call “f-stops,” it’s how we measure aperture. Most of the time you’ll see it written “f/numerical value.”

The smaller the number, the bigger the opening {the more light that gets in}.

The bigger the number, the smaller the opening {the less light that gets in}.

In other words, f/2.8 is a much bigger aperture than say f/20. I know it seems like that’s backwards, but it’s just the way it is.

I really like the diagram below, I think this helps a little, especially because it uses a real lens to bring it all together.

Oh, and another related tid-bit of information: every time you increase or decrease your aperture from one number to the next, this either doubles or halves the amount of light that gets in. If you increase the aperture from f/4 to f/2.8, your doubling the amount of light. If you decrease the aperture from f/8 to f/11 you’re halving the amount of light that will reach the sensor.

A SIDE NOTE: I can’t remember if I said this or not when I wrote about shutter speed, but if I didn’t, I’m telling you now. Shutter speed works the same way in terms of doubling or halving from one setting to the next. So, if you increase your aperture and decrease your shutter speed each by one value, the exposure would be the same in terms of light (this does NOT mean the picture would be the same, as shutter speed and aperture also affect things beyond light, i.e. blur, depth of field)

Depth of Field

Aperture has an affect on your pictures beyond exposure and it’s called “Depth of Field.” Depth of Field is how much of your picture is in-focus. If a picture has a large depth of field, then most – if not all – of the picture is in focus. A smaller aperture, such as f/20, creates a larger depth of field. Examples below:

By the same contrast, a larger aperture, such as f/3.5, creates a smaller depth of field. Often this means the foreground is in-focus and the background is blurred. Here’s some examples of a shallow depth of field:

Next up: Part 6, the final part in the series.

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