D90 focus accuracy

Started Apr 10, 2009 | Discussions thread
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Juhani Vanhala
New MemberPosts: 21
D90 focus accuracy
Apr 10, 2009

I have seen some threads commenting on D90 focus accuracy and front-focus problems, but the are a couple of questions I still havent found answer for.

To make the long story short - my D90 is having problems delivering accurate focus with 50mm f/1.4 and 85mm f/1.8 lenses. The same issue does exist also with my f/2.8 lenses, but due to deeper DOF, the problem is not that severe with them. At f/4 or above, the DOF is already so deep, that it pretty much hides the problem.

I have had my camera calibrated once, and it improved the focus accuracy so that about 65% of the shots are fairly accurately in focus even at the widest apertures. About 25% of the shots are slightly front focused and about 10% are so badly front focused that picture would in most cases be considered not worth keeping. Here is an example (100% crop) of the bad ones. Picture taken of a test target taped on a wall, kamera on tripod, f/1.8, center focus point, Single shot autofocus mode.

As a reference, here is what the lens delivers when focus is accurate:

Now to the questions:

1. Those of you who have had similar problems - have you been able to find a fix for it either by having you phone serviced or by replacing your D90 with a new one. In other words, is this a problem specific to only some units, or is this a charasteristic of all D90s.

2. I understand that no autofocus system can be 100% accurate. What can be considered as acceptable accuracy? I have seen up to 20cm front focus in some of the few hundred test pictrures I have taken lately. To me, that is quite a bit more than I would expect.

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