Photography Friday: Controlling Depth of Field

Posted by on Jul 19, 2013 in Photography | Comments


Depth of Field is a very important piece of the photography puzzle when you are trying to make compelling images. DOF is basically the distances at which your subject is in focus, relative to the rest of the photo. A wide DOF means that a large range of the photo is in focus and a narrow DOF means that a narrow range is in focus. These distances (and ranges) change based on a few things: sensor size, aperture, the focal length of your lens, and the distance from the subject.

For a visual, downloadable overview of depth of field, be sure to take a look at Craftsy’s Quick Guide to Depth of Field. Get a visual view of each f-setting on your camera and how it impacts depth of field.

There are mathematical formulas that you can use to figure all this stuff out, but I’m going to lay out some general rules, based on these four factors, so you can use your eye rather than a calculator to control your depth of field.

Camera sensor

All digital cameras have a sensor, which is similar to a piece of film from days past. The larger the sensor, the more detail the camera can capture in an image, and the more narrow the DOF. A full frame 24x36mm sensor (Canon 5D Mark II) will have a narrower DOF than a 22x15mm sensor (Canon 60D) at the same aperture and focal length. Medium and large format cameras allow for even narrower depth of field effects based on their bigger sensor sizes.

Aperture

The smaller your aperture, the narrower your depth of field will be. This seems to be the easiest part to understand. Start cranking that f-stop up (closing down the aperture) and you’ll see more and more of the image in focus. A 100mm lens at f2.8 will have a very narrow depth of field, meaning the range of focus is very small, while when you take the same 100mm lens to f10, much more of the image is in focus. You can see this demonstrated with my macro lens—nothing changed but the aperture.

Photography

Focal length

Shorter focal lengths will have a wider DOF than longer focal lengths. So, if you are photographing a person from 20 feet away with a 35mm lens, more of the image will be in focus than if you are 20 feet away with a 70mm lens, at the same exact aperture. Also, in theory, if you are 20 feet away from the subject with a 70mm lens and then move your camera to 10 feet way with a 35mm lens the DOF should remain same. Which brings us to our final factor…

Distance from subject

If your focal length and aperture are constant, the depth of field will get narrower the closer you get to your subject and wider the further away you go. Take your fastest lens (lets say aperture is f2.8) and photograph something up close. Only a part of your subject will be in focus because of the distance. Keep the same focal length and aperture and take a landscape photo or focus on something in the distance. Much more of the photo will be sharp because that range of focus is greater with greater distances.

Depth of Field

If you practice with these four factors eventually controlling your depth of field will be almost second nature. For landscape photography, where you want much of the frame– if not all– to be in focus, try using small apertures, short focal lengths, and long distances from your subject. For portraiture, where maybe you are wanting only the person’s eyes to be sharp and the rest of the face to be a little out of focus, try a large aperture, longer focal length and a short distance from your subject. Adjust each of the variables until you get just the look you want.

Which of these factors are easiest for you to control? Which are the most difficult?

Comments

  1. jgirl says:

    I am soo blessed I have came across your facebook page, I have learned so much about photography in the last few months it has really became a lot of fun to try new things to experiment with my camera.. Now because of this artical, you are wanting me to have a new camera that I can exchange for Macro and wide and now RAW images.. thank you for your professional knowledge and sharing it! Esp. for us armatures like me, who just thought turning on a camera to just point and shoot is ok! LOL I am really excited to learn more!

  2. Jason Wymer says:

    In the aperture section it states; “the smaller the aperture the narrower the depth of field”?? Surely thats the wrong way round? Great article apart from this confusion :-)

  3. poulet gloussant says:

    Jason
    He left out the most important aspect of teaching DOF, and that it that the numbers on the scale (2.8 4 5.6 8 11 16 22) are actually fractions (1/2.8 1/4 etc) of the opening of the lens. The smaller number (2.8) is a larger opening and has less in focus or less DOF than the larger number (22) which is a tiny opening and has more in focus or a higher DOF.

    In addition, the SENSOR portion of this write up should be thrown out. It’s way to technical to even think about and really won’t affect your DOF because it’s not apples to apples. Please ignore that part. Each lens has a scale (or used to) that will let you know how much is in focus. Download a DOF calculator.

  4. Clark Lloyd says:

    I agree with Jason with respect to Sensor size, the sensor will change the working focal length of the lens, leaving you with three factors for DoF, distance to subject, working focal length and aperature

  5. Carlton Ward says:

    Jason is correct and I would add that each lens has its own characteristics so you should always experiment with what you have. My long lenses work well at f/7.1 with a background 10 feet behind the subject, I will get crisp details of the subject and a beautiful blur (bokeh) behind the subject to make for a nice contrasting image. And I would add that background is crucial when composing a show, it can make or break a photo or cause much time cleaning up in post processing.

    The most important lens you have is your legs. – Ernst Haas
    Great photography is about depth of feeling, not depth of field.” – Peter Adams

  6. Leo says:

    I think it should have read aperture Value, not just aperture. An aperture value of 2.8 is small but the opening is large.

  7. Another great piece of advice, and given that DOF is so often done wrong, think this post will be really useful.

  8. Jason says:

    Another factor which effects dof is the angle of plane of focus