backfocus

Pretty much everyone got it right in yesterdays photo quiz. The problem is where the sharp area falls on the road. Today’s photo is a close-up-crop from yesterday’s shot and shows the issue more clearly. Because the camera was focused on the yellow number this should have been in focus—but instead the area behind that point is in focus—this is called “backfocus.”

I tried two Nikon D90s and both had backfocus problems; the first with all focal points, the second only with the side focal points. I did not rely only on this one photo to conclude there were back focus problems, I did dozens of controlled shots with the camera on a tripod testing each focus point against a specially designed chart that measures focus point and depth of field (DOF), and all these shots confirmed what I noticed in this photo.

It is strange that two D90s had the same problem: Perhaps it was a problem with a batch of Nikon cameras, or it might be a common D90 problem that is not usually recognized because the issue will only be visible shooting at a large aperture with a shallow DOF.

Nikon could fix the backfocus problem for me if I sent the camera to them for calibration, but being fussy I expect new cameras to work properly right from the start, so I did not go for this option. Instead I asked for a refund and the staff at Henrys (Ancaster) were very understanding and happily gave me one—they are returning the two D90s back to Nikon as defective.

So what now? Likely I will get a D300s, which because of its more advanced focusing system, will hopefully not exhibit the same problems.

The importance of having pin-point-accuracy with shallow DOF can be seen from this earlier shot taken with the D300 where the DOF was right. Notice how the subject has to be in the very narrow focused area to make a viable photograph.

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