D800 Far left/right AF issues...

Started Nov 5, 2012 | Discussions thread
Fayard
Regular MemberPosts: 127
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Re: How is this possible?
In reply to photo81, Nov 6, 2012

photo81 wrote:

Agree with that. Photographers do not use their cameras to focus on test targets in the real world. When AF sensors consistently backfocus as many as several feet or even meters behind the target, they are effectively unusable (even focus and recompose with the center point woudl be more reliable). Since I shoot landscapes these days I can probably get away with not using the edge AF points, but obviously for other uses this is a problem (e.g. focusing on someone's face off-center in the frame, at wide aperture).

RE the LumoLabs report.. I am surprised that +/- 10 AFFT is considered an acceptable deviation. From my experience (at least depending on the focal length/focus distance), even being off by 5 was quite noticeable. It may be normal according to Nikon, but why are users tolerating such poor results (especially when competing brands, and mirrorless contrast AF sensors, are more accurate)?

If anything, D800 reviewers have commented on how much more critical AF Fine tune is with the higher resolution sensor. It just kind of completely defeats the point of the high-res sensor to throw it away with inaccurate AF.

Photo81,

The problem is that most of what is said in the forums is completly useless. A focus error of 1 meter when you focus 20 meters away from your target with a 35mm lens is nothing. A focus error of 10cm when focusing at 2 meters with a 85 mm lens is way too much.

Things should be measured carefully. As we don't know enough what to expect, we are clueless. For instance, you know that the temperature of your body should be 37 C (98.6 F). When you are above by 1 C, at a temperature of 38 C (100.4 F) you can begin to considered to be sick. Nobody will think he is sick at 37.1 C (98.8 F). Therefore, for body temperature, the limit is one degree.

What is the limit, in terms of AF Fine Tune, that we should expect from a DSLR? Nobody has a clue. Falk from lumolabs has tried to do that. People seems to prefer to stick with the "I'm hot" thing and go to the physicist. I don't want to say that none of them is sick, but I think we should work on a better way.

Falk has measured many DSLR, D800, D3 and Canons and found out that an error at the DSLR level of 40 micrometers is usually found. It translates to an AF Fine Tune error of 10 for a 2.8 lens in between the AF sensors. Wether you like it or nor, it seems to be the case.

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