Depth of Field Differences Between Lenses

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By Steve Russell

Before getting into the specific subject I wanted to discuss depth of field (DOF) and why really knowing, understanding and being able to manipulate DOF can help you become a better photographer.

When we start out as photographers, especially when we get our first DSLR, about the only thing we know, and need to know about DOF is that it exists and that areas in the image that are outside the DOF will not be in focus. After we’ve taken a hundred or so photos we begin to realize that sometimes there are areas of the photo we wanted in focus and aren’t and other areas that are in focus that we wish weren’t. To use DOF to our advantage we have to do two things. First it’s important to study and understand DOF. You can’t make DOF work for you without really understanding it. It’s not difficult even though it may seem that way in the beginning. Second, we have to stop using Automatic and Program modes. In fact, most of the time the best way to control DOF is to shoot in aperture priority mode although manual mode works very well if you’re inclined to shoot that way.

What is DOF, you may ask? In its simplest form, DOF is the area in front of the camera that will be in focus. For example, let’s assume you took a photo of someone and when you looked at it on your computer there was some stuff in the foreground that was out of focus (fuzzy) and some stuff in the background that was fuzzy but the subject and the area close to the subject was nice and clear. The area that is nice and clear, from front to back, is the depth of field.

Someone else took the same photo at the same time and when you looked at their image you noticed that a lot more of theirs was in focus and you wondered why. As you might guess, the answer isn’t overly simple but it also wasn’t necessarily because you did something wrong or the other photographer did something right (or wrong). There are four variables that determine the total DOF, or the total area in front of the camera that’s in focus. Those variables are:

• The distance from the camera to the subject or the focus point
• The size of the camera’s sensor
• The focal length of the lens, and
• The aperture (lens opening)

Because this article is about demonstrating the differences of DOF between lenses, I’m going to focus mainly on the focal length of the lens, camera’s sensor size and aperture. However, keep in mind that as the distance to the subject or focus point changes, so does the DOF.

This table provides the DOF for 6 different lens focal lengths when the aperture is set on f/4 and the subject is 15 feet from the camera. It also illustrates the differences between a camera with a sensor that has a 1.6 crop factor and one with a full frame sensor.

Notice that the longest (200mm) lens has a much shallower DOF than the shortest lens (24mm). Note also that the 1.6 crop factor sensor camera has a somewhat shallower DOF than does the full frame sensor camera using the same lens. Using the short lens allows you to have almost everything in the image in focus which is one of the reasons that landscape photographers tend to use wide-angle lenses. Conversely, photographers that use long lenses, especially in the super telephoto category like a 500mm lens, usually want the subject in sharp focus and all the other things in the image to be out of focus so as not to be distracting to the viewer.

This table is the same as the previous one except that the aperture has been changed from f/4 to f/8. Here the DOF is deeper for each lens. If you were to open the lens wider to f/2.8 the DOF would be shallower.

I wrote another article on DOF on August 1, 2011, and used these same two images. By understanding DOF you can get everything in the image in focus like in the photo of the village in Central Malawi, or render everything but the subject out of focus like the thistle.

If you want to study DOF deeper and gain a better understanding, I recommend you go to Cambridge in Colour a website from the UK that has some really great in-depth information about photography. However, the best way to learn is to go out and experiment. Set you camera mode to aperture priority and take the same photo at different aperture settings (f-stop) and look at the differences. With practice, you’ll be able to visualize the finished result and set your camera’s aperture to achieve the desired result without resorting to trial and error.

Photo Credits:

Village nestled in the landscape of central Malawi by ILRI on Flickr Creative Commons
Thistle by Steve Russell on Flickr

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  • http://www.flickr.com/photos/mully410/ Mully410

    I’ve found “Simple DOF” to be a useful app for my iPod touch.  I’m mostly shooting a 500mm f4 with a 1.4x teleconveter on a Nikon 1.5 crop factor sensor.  With close up bird photography I barely have enough DOF to get the whole bird’s eye in focus sometimes, but the background, pretty much no matter what is a nice blurry blob of color. I like that. 

  • http://www.flickr.com/photos/mully410/ Mully410

    I’ve found “Simple DOF” to be a useful app for my iPod touch.  I’m mostly shooting a 500mm f4 with a 1.4x teleconveter on a Nikon 1.5 crop factor sensor.  With close up bird photography I barely have enough DOF to get the whole bird’s eye in focus sometimes, but the background, pretty much no matter what is a nice blurry blob of color. I like that. 

  • http://www.facebook.com/nakean Nakean Wickliff

    Am I completely crazy here or is this all backwards, between full frame and crop sensor!!  Don’t you have far less DOF with a full frame sensor!  At least when comparing similar images.  It makes no sense to compare this without real world situations!  If I want the same shot with my 7D(1.6crop) as my 5D(full frame)  I have to move much closer to my subject when using my 5D and the same focal length.  The distance alone changes everything!  This information might be mathematically correct, however, I think it’s missing some important information if your comparing crop sensors and full frame.  One of the reasons I want to upgrade to full frame is to get a much more shallow DOF not to get a wider DOF.

  • Steve Russell

    Nakean,

    You almost have the answer you’re looking for.  Note that in the tables, the distance from the subject to the camera is constant.  As you point out, to get the “same image” with the 5D that you did with the 7D you have to move closer to the subject.  When you reduce the distance from the subject to the camera, you narrow the DOF.

    The purpose of the article and the tables is to make folks aware that different lenses and different sensors result in different DOF.  A photographer has to be aware and should know what the DOF will roughly be in any situation.  It isn’t possible to cover every ”real life” situation in a short article just like it’s not possible to cover every real life situation in an engineering text book.

    But to answer your specific question, if you use the same lens on a small-sensor camera and a full-frame camera and shoot from different distances so that the view is the same, the small-sensor image will have 1.6x more DOF than the film image.

    However, keep in mind that if you shoot the full-frame sensor at f/8 from 15 feet you have a total DOF of 3.48 feet as indicated in the table above.  If you shoot from 10 feet to get the approximately same image, the total DOF is 1.52 feet.  The shallower DOF you’re wanting and expecting from the full-frame sensor is a function of how much closer you have to move to the subject.

  • Tony

    Your explanation is unnecessarily complex. Only two factors* affect the DoF: image magnification and lens aperture — your first three factors are all variants of image magnification. It is clearly explained on the Cambridge link you included, and further illustrated on the links on that page. It is rather tiresome to see the same myths about DoF and focal length being constantly propagated! One frustration those using small-sensor cameras face is the inability to have a shallow DoF due to the small image magnification on the sensor.

    (*yes there are some effects from pupil magnification, constant aperture zooms, etc.) 

  • James Wei

    I think the technology has done so much for our metering and DOF control automaticly.

    The traditional methodology seems obsolete these days :(