Exposure 2: Aperture

Extra explanations from the second of the A Year With My Camera online lessons.

1. depth of field in detail

Imagine you’re taking a photograph of a beach. You’re standing on the beach, pointing your camera straight towards the sunset, with a person walking away from you in the distance. Now imagine a line running directly away from you, towards the horizon. It starts at your feet, travels across the sand, and carries on all the way to the sunset, passing over the person:

aperture - depth of field 1 660.jpg

This imaginary line is called the depth of field. And the size of the aperture affects which section of that line will be sharply focussed* in your image. You can decide whether to have everything in focus in the picture, from the sand to the sun. Or whether you just want the person to be in focus.

To have a large depth of field, you choose a small aperture.

To have a small depth of field, you choose a large aperture.

aperture - large and small depth of field 660.jpg

*Technically, the depth of field is which part of the line is "acceptably sharp" to the naked eye - not necessarily what's actually in focus. The two are slightly different. However, you'll often see depth of field defined as what's "in focus". 

2: Using Aperture Priority Mode

For this lesson, ignore the fact that aperture affects exposure. Today you are just concentrating on the extra creative effect that aperture has - the ability to affect depth of field. The most common use of depth of field is to blur the background. This is achieved by making sure only the subject falls within the sharp depth of field range, and the background is outside it.

(And this is where 90% of DSLR owners give up. You are not going to be one of the 90%. Read on, understand, and enjoy.)

The next thing you are going to ignore, for today, is that your camera (actually, your lens) probably has around 20 different aperture settings. You are only going to look at the biggest and the smallest.

Before you try the homework you’ll need to find out what the biggest and smallest apertures are on the lens you are using.

1. Find your camera manual

If it’s the first time you’ve done this, first find your camera manual.

2. Next, find out how to put your camera onto Aperture Priority Mode. 

(Or just Google it. eg. “How do I put a Canon 6D onto aperture priority mode?”) Hint: for most cameras you just turn the dial that has P, M, S and A on it, to A. Or Av. ‘A’ usually stands for Aperture, not Auto. 

Do it. Put your camera on aperture priority mode. You are now off auto, congratulations.

3. Go back to the manual and find out how change the aperture.

Now, scroll through all the aperture settings from beginning to end. Write down the 2 numbers that will be at each end of the list. They might be 5.6 and 11. They might be 2.8 and 16. If you have a very expensive lens they might be 1.2 and 32.  (If you are using a zoom lens, pick one end of the zoom and do the whole exercise either zoomed all the way in, or all the way out. The min and max apertures will probably change as you zoom, and I don’t want this to confuse you.)

4. Write down the name of your lens (eg. 50mm or 35-70mm), and the smallest and biggest apertures for each.

You can find the name of your lens by looking around the front of it for a number with “mm” after it.

Time to take a break from reading. Watch this video, which goes over the entire lesson from the beginning, with examples:


If the video is not showing, click here to view

If you enjoy learning by watching, with more examples than is possible in the books/emails, you might be interested in the video version of A Year With My Camera.

I offer a limited time discount for email subscribers. For the duration of the first module only, you can claim 50% off the 6-lesson video version of the "Get off Auto" module. The aperture video above is lesson 2 in the module. The usual price for the 6 lesson module is approximately £90 (the exact price varies depending on your local sales tax, which is added at checkout). 

Ready to test yourself?

Download the quiz and the checklist for this lesson:

Now go back to the email and read about this week's project.

A Year With My Camera

If you've stumbled on this page by accident, you are reading part of Emma Davies' free beginner's photography workshop. For all the details, and to sign up, go to AYearWithMyCamera.com.