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D90 + Nikkor 50 1.4 focus problem


juhaniv

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<p>I have had D90 for some three months now, and I have been quite happy with the performance. I use mostly the 24mm f/2.8 Nikkor with it, and AF accuracy has been good.<br>

Recently I have taken some pictures with my ~3.5 year old Nikkor 50mm f/1.4m and subject has been often slightly out of focus especially when shooting wide open or in the f1.4 - f2.8 range. First I thought this was just me missing the focus point, but based on recent tests I did, it seems to be the camera/lens combo causing the problem.<br>

After taking a series of test pictures I can see the focus being somewhere 0-20 cm in front of the target. Error seems to be fairly random, but it seems that it is worse when lens has to focus from shorter end to longer end. Sometime focus is where it should be, but that is not very often.<br>

20cm error in the f2.8 or wider apertures takes the main subject completely out of the focus area, so this is really an annoying problem. I have here one test picture captured from viewNX with focus point indicator on. Picture is taken at f1.4, so the depth of field is really narrow.<br>

<img src="http://www.vanhalat.net/image/frontFocus.jpg" alt="" /><br>

I did not notice this problem with this lens when I was using it with my F100, but that was some two and a half years ago.<br>

Which one would you think is to blame on this - the camera body or the lens? What do you think could be causing this?</p>

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<p>A 20cm error seems huge to me. AF accuracy could not be absolutely perfect but pretty usable, I think. It seems to me that you have a bad focusing technique, defective lens or camera, or perhaps both. Your D90 should get focus perfectly.<br>

It could be difficult to notice focus accuracy with a 24mm lens, under certain conditions. With a 50/1.4 it is definitely easier.</p>

<p>Bruce, I find almost impossible to improve focus by eye focusing: I must accept that I`m badly eyesighted.</p>

<p>I don`t have a D90 but a D700; with my cheap 50/1.8 I have modified the standard focus point with the Fine-AF feature to get focus in the way that works to me... I like it in the closer point of DoF. Just for fun I have already checked focus accuracy at 3ft and 6ft. I have the lens tuned for 6ft. No noticeable focus shifts. Check it by yourselves.</p>

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<p>I did another test, with slightly more "scientific" methods, just to eliminate human errors from the analysis. See http://www.vanhalat.net/D90/fokusongelma.html for details.</p>

<p>I was not able to reproduce the 20cm front focus, but there was one test image with about 12cm front focus, which is bad enough.</p>

<p>When focusing from near to far, there seemed to be fairly consistent 90-110mm front focus in all pictures. When focusing from far to near, resustls were much more random: maybe about 40mm - 120mm front focus.</p>

<p>So there obviously is a front focus problem in the lens(?), which may be just an calibration issue. But what about the 80 mm variation in the latter part of the test? That is big enough error to throw subject out of focus with very shallow DOF, but is that still in the acceptable range? What level of accuracy can be considered acceptable?</p>

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  • 5 months later...

<p>I have that exact lens (50mm f/1.4) and I had the same problem with my D90 and both my D200s. I would have to stop down to about f/4 in order to get a clear picture - that is by focusing through the viewfinder. However, I found out that if you focus through Live View on the D90, you can get a picture as clear as that of a film camera.<br>

<img src="http://i214.photobucket.com/albums/cc152/asusenior/Misc/DSC_0048.jpg" alt="" /> <img src="http://i214.photobucket.com/albums/cc152/asusenior/Misc/DSC_0049.jpg" alt="" /></p>

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