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-   -   Is it the lens or camera body that demands AF fine tuning? (http://www.nanpa.org/forums/showthread.php?t=979)

Jorda75078 04-01-2013 05:03 PM

Is it the lens or camera body that demands AF fine tuning?
 
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While doing AF fine tuning (micro adjustment) last summer, I discovered a pattern. Actually, I discovered two patterns. I found that the AF fine tuning required for a specific lens would be an indication of what the fine tuning would be on another camera body, but I could not skip the fine tuning process because the camera body could also influence the final setting.

The attached table shows you the AF fine tuning settings that were required for all of my lenses on all three of my camera bodies. For all but one lens, the adjustment was positive which means the lenses were front focusing…or focusing closer to the camera than indicated in the viewfinder. However, the amount of the adjustment was not always the same from camera body to camera body.

If you study the table for a minute you will see the patterns that I saw. The settings for the D800 and the first D800e are pretty close to the same. In other words, it was the lens that was causing the AF fine tuning to be off (not result in a zero adjustment). The one exception to that pattern was for the 200-400mm lens with a teleconverter (TC) installed. I had a lot of difficulty getting a final adjustment with this lens and the 1.4x TC installed, and I subsequently do not use it very much because I don’t trust the combination.

Now look at the last column and compare it with the first column. For several of the lens, the adjustment is about 5 points less for the D800e than the D800 but the numbers follow the same pattern as the first two columns. This implies that it is also the camera mount that is causing the AF to shift and have to be adjusted. The exceptions to this pattern are the 70-200mm lens with the TC installed and the 200-400mm lens settings. These two sets of number show you why you cannot simply assume a pattern based on tests with two camera bodies and apply those same settings with another body. You have to tests every lens with every camera body.

(I will discuss the +20 that I got with the 70-200mm and TC and how I live with it in another posting.)

ericbowles 04-01-2013 08:45 PM

Larry

Thanks for sharing the data.

Based on your data, your two D800E bodies seemed to have a similar AF Fine Tune difference for most lenses. Am I understanding you that the difference is attributed to the body? And if you wanted, could be adjusted in one of the other bodies?

It also looks like the teleconverter creates some issues. The AF Fine Tuning was maxed out with the 70-200 and teleconverter. That seems to indicate a problem mating the two or some other issue.

Were the quality of focus measurements similar as well? I was thinking that its possible that one body is simply sharper - and because it can resolve more detail, it might require more adjustment but still be sharper at all measures.

Jorda75078 04-02-2013 06:02 AM

"Based on your data, your two D800E bodies seemed to have a similar AF Fine Tune difference for most lenses. Am I understanding you that the difference is attributed to the body? And if you wanted, could be adjusted in one of the other bodies?"

It appeared that each body had a built in offset for the AF fine tuning. The D800 was a little more positive than the center D800e in the table. The right D800e had a 4 to 6 point lower offset from the D800. To me, this shows that each camera body has a built-in bias for AF fine tuning. I have seen from my own experience that this offset can change. I damaged a lens last year in a fall. After I had the lens repaired, I found that I had to rerun my AF fine tuning between the camera body and the repaired lens. I also had to rerun the AF fine tuing with that same body and all of my other lens. The camera was not damaged in the fall, but the AF fine tuning bias changed.

"It also looks like the teleconverter creates some issues. The AF Fine Tuning was maxed out with the 70-200 and teleconverter. That seems to indicate a problem mating the two or some other issue."

Because the AF fine tuning with the TC installed maxed out for all three bodies and did not follow the typical AF bias pattern for a body, I would say that it is a good candidate for a Nikon repair. To my knowledge, it has never been damaged and is only two years old. However, the data shows that it is a problem.

"Were the quality of focus measurements similar as well? I was thinking that its possible that one body is simply sharper - and because it can resolve more detail, it might require more adjustment but still be sharper at all measures."

I found the quality of focus (QoF) to be about the same for both D800e bodies for each lens. However, the D800 QoF was significantly lower for each lens. When I questioned the FoCal folks about the difference, I was told that the QoF values are a relative measure for calibration only and should not be used as an absolute measure of the difference in capability between bodies. They also said that they hoped to be able to show the difference in sharpness between camera bodies in a future release...maybe version 2.0 and beyond. That was last fall. I have not questioned them about that capability again this year. By the way, I did sell the D800 after doing all of the lens tests. I knew I would not use it because I would always favor the D800e body that had extensive data showing it was sharper.


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