What's the best method for determining AF Fine Tune setting

Discussion in 'Lens Lust' started by TMR Design, Aug 2, 2008.

  1. I suppose this could or should be in the D300 forum but I thought it was more appropriately posted here in the lens forum.

    Now that I have my AF issues fixed and I know that my D300 is working as it should be, I can now take a look at AF fine tune to tweak my lenses.

    But what is the best method for doing this? I see some people using focus charts but I also see others saying setup is critical and if not done correctly you can't tell what's happening. Other people use the battery method.

    So how do you determine what AF fine tune setting is best?
     
  2. Holmes

    Holmes

    Oct 28, 2006
    Wyoming, USA
    I don't use angle charts or batteries - too many variables and to be truly accurate you'd have to map the actual AF sensor area as it compares to the little square you see in the viewfinder. They're not the same so that in itself introduces a SWAG (scientific wild-assed guess).

    I prefer to use a focus chart (old USAF version), mounted flat and perpendicular to my tripod/camera. I never adjust AFT at the minimum focus distance. Many lenses do not perform at their best at this point. I prefer to use a moderate focus distance and check the infinity focus later on which is very quick and easy to do.

    I shoot NEF, no in-camera sharpening, no auto-anything, strong natural light, extended release, and view with NX. I'll shoot 9 frames in increments of 5 on the adjustment scale. View those, pick the best, and fine tune it from there in increments of 2.

    Between each exposure, manually defocus the lens so it has to achieve a completely new focus acquisition each time.

    When I'm finished, I'll find a target at distance, usually a highway or street sign. I shoot again from a tripod and make two captures; one with AFT turned on for the lens and another with it turned off. Pretty easy to see if there's a problem at infinity.

    This procedure has worked very well for me, even on consumer zooms.
     
  3. Holmes, thanks for sharing - sounds like a great approach.
     
  4. itsmike

    itsmike

    Mar 2, 2008
    Greenlawn NY
    WOW.. I do believe the D300 Holds multiple Profiles for diff lenses.. I would like to spend a few Hours doing this one day..
     
  5. Thanks guys. I'm not going to experiment before my shoot today but I'll probably be checking out each of my lenses this week to find the best AFT settings.
     
  6. I love this feature and I'm obsessed with getting lenses set perfect to my use of the camera. I tried using focus charts, tripods, etc... What I would get would be a perfect set-up, but the lens didn't work with the way I took photos. I found this to really be a challenge when working with my better prime and zoom lenses (17x55, 85 1.4 and 180 2.8).

    What I saw was that my better prime lenses were sharp enough that it was like they could out perform the camera's AF system. I'm not trying to say anything real technical here, just that the final adjustment "felt" like the camera didn't know I wanted the CENTER of the eye in focus, it wanted to focus AROUND the eye... As for Zooms, they all seemed to need a different setting at different focal lengths and charts didn't help there either. After a TON of playing around (and I mean a ton here), I came to a different and much more fun process. One that's less scientific and works for me.

    I try to use real world situations and allow the focus adjustment process to evolve over a couple of days, rather than one quick adjustment. To get the lens corrected the first time it's put on the camera, I use my own focus chart, the magizine cover below. The sample one shown is from my lower zoom test of the new 80x400 VR I just got. I set the flash on (pop-up flash is ok), the lens set to wide open, and the camera set to a quick shutter speed (no VR). I start with the AF Fine Tune set to 0, then take a shot at +4 and one at -4, to see which one looks better.... If +4 is better, then I take one at +8 and check it against the +4 shot to see which is better. About 5 to 10 shots later I have the setting locked in. I really doesn't take long and I do it while setting on the couch watching TV with the family. When doing zooms, I use the range I plan to use the most, but I'll check the other focal lengths to see what I can expect from the lens. That gets me my initial setting and puts the lens very close to dead on. I check the focus on the same guy in the photo each time (see the circles).

    [​IMG]

    From there, I shoot the lens like crazy for a day or so and make final tweaks based on how it works in the field. I just watch the focus on photos I take and see where the focus points are. If I know that I nailed a photo, I'll check that one very close to see what area was in focus and what was not. I'll "tweak" the setting as I see real world photos turn out. Usually any final adjustments are within +/- 1 of the initial setting, but I've gone as far as -3 from initial adjustments. I think I moved my 17x55 -2 from it's initial setting, but that was because I started using the wider ranges more.

    I think you can hold only 12 different lens settings within the camera's memory.
     
  7. BandNuts & Holmes

    Great approaches. I do things exactly the same way.

    Definitely the 'over time' approach is best for me. Extreme careful analyzation of your 'in the field' real world images is key. Looking at the zone of accurate focus, and seeing where you are front or back focusing. Making adjustments to your AF Fine Tune over a few day period.

    mike
     
  8. I also do my AF adjustment like Bandnuts, Holds and Carauction.

    I like to use an image viewer (for me, PhotoMechanic) that allows me to put up two images side-by-side and scroll them independently.
    I can then do true pixel peeping and compare minute detail areas.
    For example, here's an f/2.8 shot on the left and an f/5.6 on the right from my 45P at about 42 inches (center of target at 100%, no sharpening or PP):
    [​IMG]
    Click on image a few times for full size (100%).

    The 45P is a MF lens so AF adjustment obviously doesn't apply, but it's the lens I last worked on and for which I had a side-by-side example.
    BTW, I was pleasantly shocked at how sharp this 45P was wide open. :smile:
     
  9. Glenn, one thing about PM. It uses the embedded jpeg so it's interpolating the data to show 100% - which might obscure the true detail captured in the sharper RAW file. I think PM does a great job for selecting the better of two shots for print, I'm just not sure it's up to the task for 100% comparisons for AF fine tuning.
     
  10. Thanks, Joe. I wasn't aware of that. I guess I'll take the additional step of opening my "finalists" in NX for a truer comparison.
     
  11. My pleasure Glenn. That's why PM is so damn fast. Still extremely useful since the interpolated images are great.