How-to: Improving your autofocus performance with the AF Fine Tune setting

Over the last few days and in the light of focus criticality with the Nikon D800, I’ve had a huge number of questions specifically regarding focus precision, and whether there’s anything we can do about lenses that are obviously off. Specifically, how does the AF fine tune setting work, and how does one calibrate their lenses?

1. Make sure your camera has AF fine tune. Any of the newer Nikons or Canons offer this feature, and perhaps other brands, too.

2. Find a suitably well-lit target that you and the camera can focus, and preferably one that’s flat but slightly off-plane to the camera, so it offers a variety of different focus distances. An ideal test chart is a world map on a wall, but with the camera to a slight angle to the wall (i.e. sensor plane is not perfectly parallel.)

3. Use a sturdy tripod, and set single AF. This is to rule out camera shake or false-AF movements from the camera attempting tracking.

4. Perform this test with the aperture set wide open. Stopped down, depth of field will hide focus errors.

5. If you have live view (I believe most cameras with AF fine tune do), then use magnified live view to achieve critical focus and take one shot. This will be your benchmark image – the sharpest that the lens can possibly deliver, when focused perfectly.

6. Switch back to single AF, and viewfinder mode.

7. Defocus the lens between attempts: this is important, otherwise the camera may be trying to move the focus gearing in too small an increment to overcome backlash.

8. Let the camera focus normally, and take a shot.

9. Compare the image from step 5 with the image from step 8 – if they’re the same at 100% size, then you’re fine – move on to the next lens.

10. If the images from 5 and 8 aren’t the same, then adjust the AF fine tune setting – say by 5 notches (if you have +/- 20 notches like the Nikons) and repeat 7, 8, and 9. If it’s better, keep going – do another 5-notch adjustment in the direction that created your improvement. If worse, then go back in the opposite direction. Reduce the adjustment amount changes and keep going. Basically, you want to iterate the process until you match your viewfinder-AF image with your live view focused image.

11. Save the adjustment value – if you can’t save camera settings to a card, you might want to write it down somewhere just in case.

12. Repeat for all of your other lenses.

A special note for zooms: most AF fine tune functions don’t let you input separate values for different focal lengths, so you’ll just have to try both ends of the zoom range and see which is worse; then run steps 1-12. Try to find a compromise setting that works acceptably well for all focal lengths in the range. Or, if you use one particular end of the zoom more than the other, you might want to weight your adjustment to this end of the range. MT

Comments

  1. Aw, this was an incredibly good post. Finding
    the time and actual effort to make a good article… but what can I say… I procrastinate a whole lot
    and don’t seem to get anything done.

  2. jlmphotography says:

    Question: in item number 5 should I use manual focus for test or let camera autofocus?
    Thanks

  3. Dana Wyse says:

    Hi Ming,
    Discussed with you a week ago my new D800E and 14-24 lens. Took it out shooting yesterday at Big Basin Redwood Park. Shot all photos live view, on a tripod, with shutter release cable, autofocus, iso 100, 5.6, approximate 1/8 sec shutter speed, 14mm focal length, -13 AF adjustment–but that does not matter since it was lv, Adobe rgb, AFS single point, SD in camera settings left at default, raw…..
    Bottom line, the photos just did not seem sharp. Even at the focus point they seemed grainy. Wondering if you could give me your ideal camera settings for shooting with this lens? For example, should sharpening be bumped from the default, etc….?
    Thanks,
    Dana

    • Whatever you set doesn’t affect the RAW files unless you’re using Capture NX. I use the same workflow for all my files; sharpening is done last in photoshop. I can’t think why your images wouldn’t be sharp – except perhaps that 1/8s zone tends to be a critical shutter speed for most tripods; the less sturdy ones will show some vibration. What head/ legs combination are you using?

      • Dana Wyse says:

        Benro Carbon Fibre with Really Right Stuff Medium Ball Head. Wondering if it is also possible at that setting there is just not enough light to capture as much detail in the pixels. So you would not bump up the in camera sharpening? In photoshop what would be your typical unsharp mask settings? I know that can be a lengthy subject, so just looking for what your starting point is. Thank you for any help you may offer.
        Dana

        • Hmm. Don’t know much about the tripod – stability really depends on the tube wall thickness and the rigidity of the leg locks. The Manfrotto 444 carbon I was using previously (about the size of a 190) wasn’t stable enough at those speeds; the Gitso 5-series systematic I’m using now is a rock.

          I only bump in camera sharpening because it affects the preview image, and makes it easier to check critical focus on the LCD. I zero out ACR sharpening, then start with 200%, 0.3px radius, 0 threshold – assuming you’ve got a critically sharp image to begin with, and a D800E. You should see almost pixel level detail – at least to within the resolving power limits of the Bayer sensor.

          • Dana Wyse says:

            Thanks Ming. I will check the specs on my tripod to see how it compares to the other tripod. Will also check my sharpening settings.
            Dana

          • Dana Wyse says:

            Gitzo GT-2531 Mountaineer 6X Carbon Fiber Tripod Legs – Supports 26.4 lbs (12kg) This is the same tripod as my Benro. Does this seem to unstable for the 800e and 14-24

            • The Benros are clones of the Gitzos, but the leg tube sleeves (at the joins) are much shorter, meaning less rigidity. Hard to say – I don’t see why it shouldn’t work, I’ve used my D800E on the Gitzo 1542T traveller which has a much lower load capacity.

              I’m scratching my head here. Could you post a 100% crop of the affected area somewhere?

              • Dana Wyse says:

                I could send you directly a file with a 100% crop of an area that includes the center focus point or I could post it on dpreview and send you a link to that thread. Which would you prefer?
                Thanks,
                Dana

                • Either is fine – I don’t need to see the whole file, just a crop is fine.

                  • Dana Wyse says:

                    Hi Ming,
                    I posted the photo to my thread in dpreview. Here is the link: http://forums.dpreview.com/forums/readflat.asp?forum=1021&message=42042319 Hope this helps. Could not figure out how to send the image directly to you.
                    Thanks,
                    Dana

                    • I can’t see any versions larger than about 800px wide – am I missing something? Impossible to judge from this size.

                    • Dana Wyse says:

                      Does dpreview limit the size of the image? I had to make it a jpeg using NX2 as for some reason CS5 even with ACR 6.7 will not open the nef file from my camera. Any other ideas how I can get you the image in the right size?

                    • Just crop it down to the bit you want to show me. Very odd, I’m using ACR 6.7 and it opens my D800/ D800E files just fine.

                    • Dana Wyse says:

                      Ok. Somehow this time CS5 could open the image. I cropped it to the lower right corner. Hopefully, this appears at 100% when expanded. http://forums.dpreview.com/forums/readflat.asp?forum=1021&message=42042986

                    • Most of the image looks okay to me. The extreme corner, not so much; appears to be lens issues. I haven’t seen this in any of the 14-24s I’ve used; would suggest you get it checked by Nikon.

                    • Dana Wyse says:

                      Hi Ming,
                      I had one last question for you regarding my D800E and 14-24. In a very controlled test in my office shooting at a bookcase at 4′ away, here is what I found. 14-24 at 24mm 5.6-live view far left, center and far right sharp. Same lens thru the viewfinder with -13 AF adjustment far left and center sharp far right out of focus, even bumping to -20 was a little closer but would need even more minus to get sharp. Now using my 24-85 2.8 lens at 24mm 5.6- live view far left, center and far right sharp. Same lens thru the viewfinder with -10 AF adjustment far left, center and far right sharp! I am stumped. Sure does not seem like a lens problem now, but rather a camera problem. It is also not the left AF problem others seem to have. Any thoughts. Thanks.
                      Dana

                    • It’s definitely an AF problem of some sort. Try the test again with the 14-24 at 2.8; 5.6 won’t really show any of the issues, they’ll be covered by DOF.

  4. Terry Baker says:

    Hi Ming, enjoy your articles. I have an 800e coming soon. Looking at memory cards for it. Lexar makes a 1000x card and a 600x card. Both are 32 GB. Do I really need the extra cost of the 1000x card. Thanks, Terry

    • Hi Terry, I’m using Sandisk 45mb/s Extreme Pro UHS-1 SDHC cards. The extra speed helps as you really don’t notice the buffer flush times anymore.

  5. socaltyger says:

    In reading your D800 reviews, I too was curious how you personally AF-tuned your camera to your lenses. Thanks for this simple write-up.

  6. If that was too many words, here is a video!

    • Awful video. It’s old and blares music at you while it drones on with one message after another. By the time it got around to starting the tutorial I was so tired of the music I stopped watching. What are people thinking when they make videos like this?

  7. Dana Wyse says:

    Thanks for taking the time to look into my problem. Will follow up with Nikon.

  8. Good luck!

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