Yet another DOF question

undrtow · Aug 24, 2012

So I just bought a nikon d3100 and have really enjoyed playing around with it. I've been reading a ton on this website and others trying to better understand my camera and photography. I have been especially trying to wrap my head around DOF as it seems to be a critical aspect of photography.

Anyway, I'm just trying to understand how to ensure that the subject is INSIDE the DOF, resulting in a sharp subject. Is this done simply by focusing on the subject? Or is there a set-in-stone focus distance within a DOF for each particular aperature and focal length, meaning that the subject needs to be placed in that particular DOF? I think I've just read so much on the subject in the past day or two that I'm having trouble assimilating it all in my mind.

Anyway, I'm hoping this makes sense, as the more I re-read it the less clear it sounds. Thanks in advance guys.

KmH · Aug 24, 2012

Check out the DoF and other basic concept tutorials here- Learn Photography Concepts

You can plug different numbers into the DoF calculator to get a feel for how it works.

Here are a couple other online DoF calculators: Online Depth of Field Calculator

I really like this one because of the way it shows the focus sharpness fall off - http://www.tawbaware.com/maxlyons/calc.htm

Designer · Aug 24, 2012

undrtow; I'll take a stab at it. The DOF refers to the range most people would consider "in focus", although technically perhaps not perfect focus. The range depends on the focal length of the lens, and the aperture, and can be found in tables or calculated. When you focus on a three-dimensional object, part of it will be at the point of your focus, part of it will be in front of the focal plane and part of it will be behind the focal plane, but the tables will tell you that everything in that range will be "in focus".

So let's say you are taking a picture of a group of people. Some in the middle will be in very good focus, the ones in front may or may not be in focus (depending on the focal length and aperture) and the ones behind may also be in focus (or not, depending).

When you are calculating the DOF, take your variables, measure the distance, and you can tell beforehand if everything will be in focus.

undrtow · Aug 24, 2012

Thanks for the guidance. The DoF calculators help to reinforce what I was thinking. I think I just got confused when reading a post where someone made the comment that the depth of field was a few feet behind the picture's subject. I'm assuming that happened because the photog somehow focused behind the subject? Is there any other way that the DoF can lie behind the intended subject?

SCraig · Aug 24, 2012

undrtow said:
Thanks for the guidance. The DoF calculators help to reinforce what I was thinking. I think I just got confused when reading a post where someone made the comment that the depth of field was a few feet behind the picture's subject. I'm assuming that happened because the photog somehow focused behind the subject? Is there any other way that the DoF can lie behind the intended subject?

No, it wasn't a mistake. Depth of field will ALWAYS extend behind the point of focus. You have to remember that DOF is a RANGE, not a POINT. It generally extends from 1/3 in front of the point of focus to 2/3 behind the point of focus. If, for example, you had a 6' depth of field it would extend from approximately 2' in front of your focus point to 4' behind your focus point.