Depth of Field

In the last post, I left off after talking about the effects of aperture on light. Now I am going to talk about depth of field. This is where we come to the point of why aperture is so important.

While you can use the aperture of your lens to let in more or less light, you can also use aperture to change the depth of field.

Before I talk about depth of field, let's talk about the plane of focus.

Hold your hand close in front of your face so that you can focus your eyes on your fingers. Do you see how the background behind your hand is blurry? 

Next, shift your eyes so that you're focusing on the background. Your hand is now out of focus.

Cameras in general work in a similar way. The object that the camera is focused on creates a plane of focus. Other objects in front of and behind the plane of focus won't be as sharp.

Now here’s the thing about aperture, you can set it so that things in front of and behind the plane of focus do appear perfectly clear.

Below is a series of diagrams illustrating the effects of aperture on depth of field using the example of a football field:

Imagine that you're standing on the zero yard line looking down the length of a football field.

You focus on a football sitting on the 25-yard line. That's the plane of focus.

In the first case, the aperture of the camera is set to f/2.8 (wide open). An aperture of f/2.8 creates a very shallow depth of field which is shown by the grey area. In this case, only the football will be in focus. Everything in front of it and behind it will be blurry.

The next example has the aperture set to f/8.0 (somewhat open). Now the football is in focus on the 25-yard line, but objects on the 20-yard line and the 35-yard line are also in focus. You've increased the depth of field.

Finally, you set your aperture to f/22 (stopped down). Now everything from the 10-yard line to the 75-yard line is in focus.

So to sum the diagrams up, the higher the aperture setting, the deeper depth of field will be while the lower the aperture setting is, the more shallow the depth of field will be.

So how can all of this be applied to when you actually take photos?

Let’s start with a shallow depth of field. A shallow depth of field (f/2.8 to f/4) is good when you are 

taking a portrait and don't want the background to compete with your subject. Wide apertures ensure that the entire background is blurry.

Now let's say that you're taking a group photo, with 2 rows of people. Do you really want the people in front to be in focus and the people in the back to look blurry?

Probably not right?

So what you will need to do in this case is to narrow your aperture (and increase your depth of field) so that everyone in the photo looks crisp.

As for landscape photographers, they tend use narrow apertures (f/11 to f/22) to ensure that everything from foreground to background is in focus.

This makes the landscape look natural. What I mean by that is when you look at a landscape, your eyes are able to see the whole scene, without any part of it being blurry due to a shallow depth of field. Landscapes taken with wide apertures and shallow depth of field just don't look the way you expect them to.

Adjusting aperture can also be an aesthetic choice.

Imagine that you are taking a shot of a flower in the desert. If the desert background is unappealing, then you can use a wide aperture (f/2.8) and shallow depth of field to blur the background and isolate the flower.

If the desert background has a lot of pattern and will really establish the location of the flower, then a narrow aperture (f/22) and a wide depth of field will capture the entire desert scene.

This is pretty much everything you need to know about aperture for now and hopefully you should  have a pretty good handle on what the aperture setting does:

1. Aperture can be wide or narrow
2. Aperture affects the amount of light that passes through the lens
3. Aperture helps you control depth of field

The best way for this to sink in is to go out and practice. Set your camera to aperture priority mode and take picture after picture, changing aperture for each one.

The nice part about digital photography is that it accelerates your learning curve. Since you can delete all of the photos that you don't like, you have the freedom to take hundreds of shots without spending tons of money on film.