Depth-of-Field - It's More Than Aperture

September 6, 2017

 

Depth-of-field is one the best ways to add creativity, interest, and style to your photography. Good news is that the principles behind your depth-of-field aren't too difficult.

 

Depth-of-field refers to how much of a photograph is in sharp focus from foreground to middle ground to background. A photo with a deep depth-of-field will be sharp and in focus all the way from foreground to background. A photo with a shallow depth-of-field will have a sharp subject and blurred out elements in front of or behind the subject. Look at the photo above. Would you say that the photo has a shallow or deep depth-of-field?

 

Your answer should be "shallow" because the foreground and background elements are not in focus while only a sliver of the middle-ground is in focus. If the photo above had a deep depth-of-field, then more of the little screws would be in sharp focus.

 

Adjusting aperture was the first way I learned how to control my depth-of-field in a photograph. (You can read more about aperture here.) But depth-of-field is affected by more than just your aperture setting. You have to consider two other things: the focal length of your lens and the distance between you and your subject.

 

Here are the two basic ideas to remember:

  1. When you use a short focal length (a wide angle lens like 16mm or 24mm), your depth-of-field is much deeper than when you use a longer focal length (a zoomed-in lens like 85mm or 200mm).

  2. When you are close to your subject, your depth-of-field will be much more shallow than when you are far from your subject.

Remember, you have to think about three variables when thinking about your depth of field: 1. aperture, 2. distance, and 3. lens focal length.

 

To help you understand how the three variables affect depth-of-field, I'll provide a few example photos and some numerical examples using this depth-of-field calculator.

 

APERTURE

 

Let's consider aperture first. You'll remember from my previous article that a wide aperture (a smaller f-number like f/1.2 or f/2.8) gives you a shallow depth-of-field while a narrow aperture (a larger f-number like f/11 or f/16) gives you a deep depth-of--field.

 

In the series of photos below, I kept constant the focal length of my lens and the distance between my camera and the red bench. The only variable I changed was my aperture. The first difference you should look at is the foreground. Notice how blurred the ground is at f/4 compared to how sharp the ground is at f/16. The photo at f/4 has a shallow depth-of-field, and the photo at f/16 has a deep depth-of-field. 

 

 

 

One fun side-effect of the aperture change is the sunburst you see between the two trees. If you ever wondered how to create a sunburst, now you know! Use a narrow aperture (like f/16) and make sure the sun is close to the edge of a physical object (like the trees). The sunburst won't be as good (or exist at all) if the sun is just floating in the sky.

 

If you're interested in numerical comparisons, here are some calculations based on a full frame camera with a 50mm lens and subject that is 10-feet away. Here's how changing your aperture affects your depth-of-field:

 

- at f/2.8, your depth-of-field is 2.1 feet

- at f/4, your depth-of-field is 2.9 feet

- at f/8, your depth-of-field is 6.3 feet

- at f/16, your depth-of-field is 17.2 feet

 

DISTANCE

 

Now let's consider the distance between you and your subject. In the first set of photos to follow, I kept constant the focal length and the aperture. I just moved my camera back a foot or two with each photo while continuing to focus on the same part of the stack of books.

 

Here are the photos straight-out-of-camera:

 

 

The photos above make the difference in depth-of-field tough to see. Since the perspective and composition change, the difference in depth-of-field is hard to notice. That's why I used books for this comparison. The small letters on the books make the difference easy to see once I crop the photos to show the same composition. Here are the same photos, cropped to match:

 

 

 

See the difference now? Compare the quantity of letters in focus in each photo. Fewer letters are in clear focus in the top image than the bottom image. Therefore, when the camera is closer, the depth-of-field is shallower than when farther away. 

 

For the numerical comparison, here are the calculations based on a full frame camera with a 50mm lens set to f/4. Here's how changing the distance between your and subject affects your depth-of-field:

 

- when your subject is 5-feet away from you, your depth-of-field is 0.71 feet

- when your subject is 10-feet away from you, your depth-of-field is 2.9 feet

- when your subject is 20-feet away from you, your depth-of-field is 12.7 feet

- when your subject is 50-feet away from you, your depth-of-field is 155.7 feet

 

FOCAL LENGTH

 

Finally consider focal length. In the first series of photos below, I kept constant the aperture and the distance between my camera and the books. I just changed the focal length of my lens for each photo. (I used my Canon 24-70mm f/2.8 lens.)

 

Here are the photos straight-out-of-camera:

 

 

Again, the photos above make the difference in depth-of-field tough to see. Just like with the distance comparison, the perspective and composition change, so the difference in depth-of-field is hard to notice. Again, that's why I used books for the comparison. Here are the focal-length photos, cropped to match compositions:

 

 

I'm sure you see the difference now. Compare the quantity of letters in focus in each photo. Fewer letters are in clear focus in the top image than the bottom image. Therefore, when the focal length is longer, the depth-of-field is shallower than when focal length is shorter. 

 

For a final numerical comparison, here are the calculations based on a full frame camera with the aperture set to f/4 and a subject that is 10-feet away. Here's how changing your focal length affects your depth-of-field:

 

- when you use a 24mm lens, your depth-of-field is 20.9 feet

- when you use a 50mm lens, your depth-of-field is 2.9 feet

- when you use a 100mm lens, your depth-of-field is 0.71 feet

 

What The Examples and Numbers Tell Us

 

What should you take away from this article if you're just beginning to learn about depth-of-field? Here are some tips and ideas for different genres of photography:

 

If you're creating a landscape photo, then you're usually using a short focal length, something between 16mm and 35mm. That means you can open your aperture pretty wide (perhaps f/2.8 or f/1.4) and still maintain a wide depth-of-field. A wide depth-of-field would keep foreground, middle ground, and background in sharper focus, which is usually a goal of a landscape. You just have to make sure that you focus on something that is a decent distance away from your camera.

 

For example, according to the depth-of-field calculator, if you use a 24mm lens on a full frame camera, you can set your aperture to f/4 and focus on something 22-feet away to get infinite depth-of-field, which means everything from foreground to background would be in focus. (Want to really make sure your entire landscape is in focus? Start reading about hyperfocal distance.)

 

If you're creating a portrait, then you're usually using a longer focal length, something between 85mm and 200mm. Portraiture, especially out in nature, often looks good with a shallow depth-of-field, so you can shoot at a wide aperture, too. A wide aperture on a long lens provides a shallow depth-of-field. Just keep in mind how distance affects your depth-of-field, especially in a group photo. With a group photo, you'll want to have 4-to-5-feet in clear focus. Why? Chances are, you won't be able to line everyone up on the same focal plane, especially if children are involved.

 

For example, if you use an 85mm lens on a full frame camera with an aperture of f/5.6, your group needs to be about 15-feet away to get a depth-of-field of more than 5-feet, and that doesn't leave much wiggle room. And what if you want a more blurred background? The easiest way to do that is to create distance between your subjects and what's behind them.

 

Let's consider macro and other table-top photography. Remember what happens when your subject gets closer? The depth-of-field decreases tremendously. For detail shots and other table-top product photography, I use a macro lens with a 100mm focal length and a minimum focusing distance of one-foot. That means the closest something can get to my lens and be in focus is one-foot. If I use that distance and an aperture of f/16, then my depth-of-field is only about 2 inches. At f/2.8, my depth-of-field is almost immeasurable. That's a main reason why macro photographers use tripods and combine multiple images to make a photo.

 

ONE LAST TIP ABOUT APERTURE

 

While not entirely related related to depth-of-field, I wanted to complete my two-part series about aperture and depth-of-field with this last piece of knowledge. One thing you can do to help you choose an aperture is to memorize this sequence: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. That sequence is the standard sequence for aperture. Each time you move to a larger aperture (lower number) in the sequence, light doubles. Each time you move move to a smaller aperture (higher number), light cuts in half. That's what photographers mean when they talk about a "stop" of light. Changing from f/2 to f/1.4 is "opening up a stop," which means you've doubled the amount of light entering your camera by widening your aperture by one "stop of light."

 

Most cameras allow you to change aperture by 1/3 with each click or turn of the wheel. That means three clicks in the same direction of your aperture adjustment wheel changes your exposure by one stop of light, either doubling the brightness or decreasing the brightness by half depending on the adjustment you make. Don't forget: you'll also increase or decrease your depth-of-field, too.

 

There you have it! You now know the three basic principles behind depth-of-field: 1. aperture, 2. distance, and 3. lens focal length. Set up a scene for yourself and start experimenting. Nothing will improve your photography faster than deliberate practice. 

 

Aaron Taylor is a stay-at-home-dad and professional portrait and product photographer. Aaron is forever blessed to be in love and married to his best friend and partner in parenting. Most of his time is spent chasing his curious, energetic kids, a three-year-old son and one-year-old daughter. Aaron lives in Columbus, Ohio. Before moving to Columbus in the summer of 2016, Aaron was a high school English and Drama teacher in Montgomery County, Maryland. He spent ten years in the classroom and earned National Board Certification in English Language Arts. Give him his family, a good cup of coffee, and a homemade cookie or three, and all is right in Aaron’s world.

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