Major frustration in D800 AF Tuning even with DotTune Method

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Major frustration in D800 AF Tuning even with DotTune Method
6 months ago

I'm trying to AF Fine Tune my D800 with various Nikon lens using DotTune method developed by Horshackdescribed in his youtube video DotTune: Autofocus fine tuning in under 5 minutes http://youtu.be/7zE50jCUPhM

Initially I followed the steps strictly but I found very unpredictable results. Then I read through every threads on the http://www.dpreview.com/forums/post/50883023

Based on the info I learned, I modified the steps slightly to try addressing the issues I'm seeing. But it is still giving me lots of problems. So instead of 5 mins AF tuning, it turns into days. It is so frustrating and I hope that you guys could give me some help.

How I set it up:

I put my target (Bob Atkin's focus chart suggested by Horshack) on a white wall in my studio. I use the 2 modeling lights with my speedotron with 2 softboxes attached to ensure the target had the proper contrast. And the target has consistent lighting to avoid any variation with the lights. I put my D800 on a Bogen 3221 professional tripod without using the center pole to minimize any camera shake. I use the levels on my Bogen tripod head and the virtual horizon on my d800 Liveview to ensure the camera is level correctly and pointing squarely to the target. Set the camera to focus only using AF-ON button.

Here are my steps:

  1. Set the camera on the tripod at a distance using a tape measure
  2. Make sure the AF Tune is set to 0 and using the AF-S and with the center focus point
  3. Establish critical focus in Live View by zooming in 100% with the AF-On Button
  4. Evaluating Viewfinder Focus Confirmation by counting to 10 for having the solid green dot (I made sure I only touch the shutter release button very lightly to avoid shaking or moving the camera)
  5. Cycle AF Tune values to find the edges of the range
  6. Repeat testing the point surrounding the edge values to ensure the same result could be repeated 3 times in a row
  7. Mark down the edge values on paper
  8. Repeat the same steps for 3+ times to until similar edge values are recorded with previous tests at that distance
  9. Move my camera to another distance and repeat 1-8 again.
  10. Put all the data in Excel and had it calculate the miidpoint on each test run.

Here are my results for one of the lens - Nikon 135mm f/2.0D AF DC-Nikkor Lens. Based on previous testing, I found that I need to set it to +2 using the Defocus ring or it will be completely out of +20 range.

As you could see the calc AF mid point range from 6.5 t0 -3.5. So it is a very wide range. I'm not done with the testing yet but want to make sure I'm doing it right before continue spending hours in this. While I only showed the results of this one lens, other lens (except the Nikon AF 24-70mm f2.8 which is my most recent purchase) have similar results.

What AF Tuning point should I use for this lens? What did I do wrong? Is my D800 just having focus problem and need repair? Or my lens are just too old and not suitable to use DotTune?

Some footnotes:

1. Why I chose these distances? Because they are 50x of the focal length of the lens that I own. Given my previous bad results, I decided to test all lens with all these distance as I don't really shoot just one distance anyway.

2. My understanding is that shortest focus distance will have the least DOF. It seems to me that if we need to achieve best AF point, we should use the shortest focus distance. And I don't think I typically shoot so far away for a particular len but I went along with 50x anyway. If someone could help explain why use 50x, I would appreciate that too.

Thanks a lot for reading this long post and thanks in advance for your help and suggestions.  I very much appreciate that.

Joshua

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Just trying to improve my draft one image at a time
You could check our more of my photos at http://www.joshuaphotographystudio.com

Nikon D800
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