Intermediate Depth-Of-Field Lesson – The Difference in DOF Between Wide & Telephoto Lenses

(Note the killdeer (Charadrius vociferous) picture used above was shot with a Canon 1D MK II N and Canon 600 f/4 IS lens with Canon 1.4 teleconverter (EFL 840mm) handheld laying on the ground and shot at f/8. The DOF was less than one inch at 26 feet – hence the VERY skinny DOF leaving the photo blurry in front of and behind the bird. FYI there was a big outhouse behind the bird about 100 feet away that just disappeared because of that skinny DOF.)

This post is primarily aimed at people who use long glass – say 135mm and longer – but it will benefit any photographer.

When you are talking about depth-of-field, the practical reason for the discussion is to discuss the near limit of acceptable sharpness and far limit of acceptable sharpness. In other words, the part of an image that is in focus, front to back, based on the photographer’s selected focus point.

When I first got into photography, I was taught that you want to assume that your depth-of-field starts about 33% of the way into the scene (at the focus point) and ends about 66% of the way into the scene (unless you are focused on infinity.)

Turns out that it’s a popular misconception that depth-of-field is always 33.3% in front of point of focus and 66% behind the point of focus. That is absolutely most often true in the case of standard and wide-angle lenses, and in situations where the subject to camera distance is more than 50 feet, but NOT true at all when you start to shoot with telephoto lenses and/or close subjects. Perhaps the single most neglected factor in these discussions is subject to camera distance. Subject to camera distance and lens focal length impact what the area of acceptable sharpness will be – every time.

If you read my post One Of The Most Misunderstood Things About Depth of Field, you know that – as camera to subject distance increases, depth-of-field increases. But remember the inverse is true. As camera to subject distance DECREASES, depth-of-field decreases.

When I use big glass like the Sigma 150-600 zoom, I am often working at 600mm. When I shoot with a big telephoto AND I work close – i.e., at the lens’ close focusing limit (8.5 feet in the case of the Sigma 150-600) DOF becomes VERY, VERY, VERY thin. In some cases the DOF can be near ZERO! Yep, it’s true.

But back to my main point. With the big glass, especially when focused at less than 50 feet, DOF is NOT 33/66 – it’s more like 50/50. With telephoto lenses you get depth-of-field that will be an equal amount in front of and in back of the focus point.

Why does this matter? When shooting landscapes with a wide angle lens for instance, you will often put your main subject in the DOF sweet spot – knowing that you have about 1/3rd in front of the focus point to 2/3rds in back of the focus point with which to find that sweet spot. If you do that when shooting a big telephoto lens, the area of the image that you want highlighted will be wrong. It’s 50/50 not 33/66. Is this confusing? Yes it can be so that’s why I like to point people to an amazing and free resource I found called simply DOFMaster.

Use this website to learn more about this subject. It’s worth 10-15 minutes of your time. Here’s how:

Select your camera body. Type in the focal length (mm) of the lens you want to learn about. Select an f/stop, and select the subject distance.

You can prove out every theory I proffer here instantly.

I am using a Canon 1DX for this test. I select a 600mm focal length, an f-stop of f/8 and a subject distance of 10 feet. In that scenario, my DOF is a mere 0.3ft and that 0.3 feet is spread out 50/50.

Remember that as camera to subject distance increases, depth-of-field increases. Type in 100 feet instead of 10 feet and you’ll see that the DOF moves from 0.3 feet to 3.99 feet! Type in 1000 feet and the DOF jumps to 423 feet at f/8 but the split moves to a 40/60 split.

These concepts may seem vague but they are important. Over time, if you get to be as old as I am, you eventually learn this stuff and just end up knowing what your DOF will be in most situations. But for now, use this DOF calculator to learn it. And remember the concepts.

If you work at close focusing distance with long lenses you will have razor thin DOF and it will generally be evenly split 50/50. This holds true even at very small apertures.

I hope this helps.

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Filed under: Photography, Shooting Tagged: depth of field, Scott Bourne, telephoto lens