What are Apertures? Depth of Field?

How to improve your pictures by understanding
this powerful, but overlooked camera feature

By Marion Owen, Fearless Weeder for PlanTea, Inc. and
Co-author of Chicken Soup for the Gardener's Soul


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Love letter

Dear readers, depth of field is NOT how deep you plant your potatoes!

Yes, for 20 years I've taught photography classes and seminars I've learned that apertures are one of the least understood, yet one of the most useful camera controls.

By making friends with apertures, you'll see dramatic improvements in your photographs. And I know thousands of students who will tell you the same thing.

What's an aperture?

The aperture, or lens opening, is one of the controls you can use to adjust the amount of light that reaches the film. Shutter speed is the other control. Turning a ring on the outside of the lens (pushing a button on some cameras) changes the size of the lens opening. In an automatic setting, the camera does this for you. Apertures, also called f/stops, are like the iris of your eye, in that the opening can get larger (open up) to let more light in, or it can get smaller (stop down) to increase the amount of light.

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Aperture settings appear as numbers that read like:
22, 16, 11, 8, 5.6, 4, 2.8, etc.

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In addition to exposure, the size of the aperture opening also affects how much of the scene you are seeing through the lens will be sharp in the finished picture. This area of sharpness is known as depth of field. Understanding how aperture affects depth of field is one of the keys to making "keeper" photographs versus so-so ones. The best way to explain this of course, is through photographs...

Photo showing wide depth of field Photo showing shallow depth of field
Wide depth of field (left) and narrow depth of field (right)

In the photo on the left, everything is in focus, from the poppies in the foreground to the person at the top of the frame. Here, the depth of field is very large. In the photo on the right, only the flower is in focus. The area behind it and in front of it is out of focus. In this case, the depth of field is relatively small, or narrow.

Your camera manual describes apertures in more detail, but here's what you need to remember for this lesson: The larger the number, the larger the depth of field. That is, the more will be in focus. The photo on the left was taken at an aperture setting of f/22 while the one on the right was taken at f/5.6.

The photo on the right illustrates another attribute of depth of field: The ability to isolate your subject. Thus, if you have a busy background, you can throw it out of focus by selecting a narrow depth of field. Have you ever seen a photograph of say, a bride and groom at the alter? Everything looks lovely, as one would expect, until you look closely at the photo. Oh no! The flowers are coming out of the bride's ears! Had the photographer selected a different aperture, he or she could have eliminated the busy background.

Speaking of fixing the background, let's look at two more real-life examples. In the left photo, taken at f/16, the background in the upper left hand corner is busy and blotchy, stealing your attention from the rhododendrons. By selecting an aperture such as f/4, the background is thrown out of focus. By isolating your subject like this, you're telling the viewer "look at this."

Photo showing wide depth of field Photo showing shallow depth of field
Busy background (left) is improved with a narrow depth of field (right)

Now, here's your homework assignment: Next time you go out to take pictures, experiment with depth of field. Take two or more photos of the same scene, using different aperture settings. Placing your camera on a tripod will make life easier. Remember to take notes so you can refer back to them. You can find more photo tips on my page of articles.

Thanks for visiting and please stop by again. I'll put the coffee on!

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