Learning from one's blurred photos: where was the focus point set?

Question

After some shooting, I inevitably find that some photos (and by Murphy, often the best ones) have a blurred subject.

Even if the shots are spontaneous and hence the subject is hardly static, I imagine that selecting shutter priority at 1/200sec. is a guarantee against blurriness resulting from motion (as opposed to limited depth-of-field and incorrect focus).

My question is: Is there a way for me to see where I have set the focus point to determine whether that was the mistake? I am using a Nikon SLR with processing on OS X. Needless to say, available light limits how narrow an aperture I can choose.

Answer 1

ViewNX 2 will tell you your active focus point(s). (And EXIF contains focal length info, if you are interested in that, by any chance...)

Answer 2

Most camera manufacturers include such functionality in the software they provide with their DSLR cameras. Since you are shooting Nikon, ViewNX should provide such an option.

A couple of things to keep in mind when analyzing photos with regard to auto focus performance:

• If you lock focus and then recompose before taking the shot any application that displays which point was in focus will not show you where that focus point was aimed during focus lock but only where it was aimed when the shot was taken.

• Many DSLRs, especially those with a lot of AF points, use active focus areas for each point that are much larger than the point itself is displayed in the viewfinder. The AF system will focus on the highest area of contrast in the entire area of sensitivity for a given focus point, not just the area directly over the little square in the viewfinder. See Andre's blog for a real world example of how this can result in missed focus. Although the camera in question is different the principle discussed in this answer and this one is not.