AF fine tuning (D800E) strange behavior...

Discussion in 'Nikon' started by dror_guy, Jul 4, 2014.

  1. Hi all,
    I'll start by saying that I have no focusing issues anymore (seems like it at least) but something is very strange with how the AF fine tuning works and I wonder if anyone has come across this... (Apart from that I assume it might cause problems in the future)...
    So I purchased a new Nikon D800E a few weeks ago and getting accurate focus was very hard especially at max aperture... so I only used f/4 and higher. The sharpness was still acceptable but not enough to my mind.

    Anyway, yesterday I decided to look at the AF fine tuning and was amazed - I had a really serious back focus with all of my lenses! (so it's probably a camera issue).
    So I worked tethered with lightroom and zoomed in 1:1 on an object I photographed (it was simpler then using a ruler although I did that too). The shots were made with maximum aperture on a good monfrotto tripod.
    Took around 200 shots on all of my three lenses and carefully checked each image with different fine tuning values until I saved those three values:
    24-70 2.8G: -16
    50 1.8G: -14
    85 1.8G: -16
    So now's where things got strange - I've retested and re-edited the values I saved... the first shot with the saved value (before any re-edit) was ok. Then i changed from -16 to 0 (24-70 lens) and still the same (in the first tests it was completely out of focus), then to +20 and out of focus then back to 0 was good but back to -16 was out of focus (that's the value that should be good)... Then I switched the AF fine tuning OFF and still perfect focus (before I first touched the AF fine tuning that setting gave clear back focus)... Same thing with all other lenses so I simply deleted all saved values, but still focus is perfect with AF fine tuning turned either ON or OFF...
    So I assume the values were stored some where but not completely deleted (unless I got the something wrong - but I really worked hard on this...). Or maybe they will be deleted sometime in the future when I do a complete setting restore in the camera or something like that...
    Anyway, the thing that is really bothering me is that it's obvious that the camera has a back focus and if the AF fine tuning values that I saved and deleted were still stored and saved for these particular lenses then it's not going to solve the actual problem - which is the back focus of the camera... further more, I deleted those values but they weren't actually deleted...
    Anyway, I wondered if anyone has come across this AF fine tuning behavior...
    Thanks in advance,
    Dror
     
  2. What target were you using and what method were you using to analyze the results?
     
  3. small box of my black rapid belt and focused on the face of the girl on the box...
    visually analyzed the shot 1:1 tethered on lightroom...
     
  4. Are you focusing with the optical viewfinder’s Phase Detection AF system? AF Fine Tune is only applied to PDAF/eye level focusing, not to Live View or tethered focusing, where focus is determined solely by the contrast detected on the CMOS imaging sensor. AF Fine Tune corrects for the mismatch between the mirror and PDAF sensor and the CMOS. Images focused in Live View or by computer controlled live view need no correction because focusing is done on the image-capturing sensor itself.
     
  5. "small box of my black rapid belt and focused on the face of the girl on the box..."

    That explains a lot of your inconsistency.

    For starters this really does work best with a target designed for AF micro-adjustment setting - I prefer the LensAlign Mark
    II used with the same company's FocusTune software http://www.lensalign.com, but there are other off the shelf. Products
    and some people make their own targets - and testing protocol.

    If you don't want to pay for an OTS product you can make your own. You need a flat target and a ruled scale. The scale
    needs to be at a 45 degree slope and the target should have strong contrast while the scale should have very small but
    clearly readable and evenly spaced delineations.

    Protocol: Nikon (and Canon) recommend the target be at 50x the lens focal length while Michael Tapes of LensAlign and
    WhiBal recommends a 25x focal length distance. From my tests at both distances I recommend the 25x FL distance. The
    target needs to be parallel -not sort of parallel but truly parallel- to the camera's sensor. Shoot at -20, -15, -10,..., +20 AF
    micro-adjust settings, and shoot five frames at each of those settings, defocusing slightly each for each frame. Figure out
    which grouping look best and then shoot a second round of five frames each at single increment steps around the
    adjustment number that looked best. So if the adjust that first looked is -5, shoot at -3, -4, -5, -6, and -7. Two more things:
    camera is tripod mounted and do it n good light.

    I know this sounds like a boring as hell process and honestly I can think of many things to do that are more fun, but it
    does work. And the LensAlign + FocusTune combination really does speed things up and takes a lot of the guess work
    and uncertainty out of the process.
     
  6. I'm sure that there are some nifty gizmos for fine tuning, but I use a page of printed text - typically from a magazine - taped flat to a wall. I compare Phase Detection autofocus at various Fine Tune settings to the results of Contrast Detection autofocus in Live View - which, when used properly, is extremely accurate. I've been using this approach for a couple of years with excellent results.
    Fine-tuning Suggestions:
    1. Make sure that you're setting the "Saved value" rather than the "Default" value on the autofocus fine tuning page for each lens.
    2. Make sure that you press "OK" after each value change, or the change won't be saved properly.
    3. Take are least three shots are each AF fine tune value (e.g. three shots at -5, etc.) and compare them. Phase Detection AF can give slightly different results from exposure to exposure, so it's best to average a group of them.
    4. Review the results on your computer using View NX (viewed at 100 percent), not on your camera's little LCD screen. The larger the monitor, the better.
     
  7. Dan's method works as well. You just need to make sure the camera is square to the page.
     
  8. pge

    pge

    Try this method LINK and compare your results.
     
  9. Alternatively you can use a camera oriented at an angle to a ruler or similar scale target, focusing on a particular point on the scale. A good target for this method can be found here: http://regex.info/blog/photo-tech/focus-chart This target has a line for focusing with light grey numbers nearby that the PDAF sensors ignore. Also in this method, you do not have to worry about getting the camera and tripod perfectly positioned, it just needs to be at an angle, such as 45˚ or 30˚ to the target. The angle isn’t critical.

    Lenses vary quite a bit in how much AF Fine tune they need. On my D800E, my Zeiss ZF.2 lenses all require 0 as does my old 85mm/1.4 AFD lens. My 28mm/1.8 G AFS requires -17. Your numbers will vary, due to +/- tolerances in cameras and lenses. Zeiss deserves kudos for better consistency and tighter tolerances than Nikon uses.
     

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