Saturday, September 3, 2011

D7000 and 70-300VR – How is the auto focus?

There is a thread running right now at DPReview regarding this issue. Someone tested the 70-300VR on the D5100, which is the next model down but with the same sensor. He was wondering how this lens handled the very high pixel density of the D7000.

He said he got a lot of blurry images, even though his D700 shot this lens perfectly. So I thought I would test it on my D7000, since my copy of this lens has been perfect on the D700 and the D300.

I also noticed (again) that the metering in live view appears to underexpose images considerably when compared with normal view through the OVF. I have no idea why, but perhaps the subject area is wider when in live view for whatever reason.

OVF with Phase Detect AF

That looks pretty sharp to me.

Live View with Contrast Detect AF

That also looks sharp. But the image is slightly magnified and is underexposed by a stop. No idea why, since I did not shift positions at all and I focused on the same spot.

Here are the 100% crops to show any difference in focus.

Very similar. The nod goes to contrast detect for the crisper edges. But this is an image at the equivalent of 46 inches wide … so this difference is not all that relevant. Of course, when shooting people with hair, this difference does make a difference if printing big. So fine tuning AF is worth the effort. In studio, though, I would be pretty tempted to focus using contrast detect in live view.

Bottom line is that my 70-300VR copy appears pretty good on this camera. If one is seeing blurred images, one should try it in live view with contrast detect focus. Precision over speed to test the lens.

Then try to adjust AF Fine Tune if there is a massive difference in focus between the two methods. The D5100 does not offer AF Fine Tune, so that would be a real problem if the lens will not AF. But this is still not a resolution issue.

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