Steve P: Auto fine tune query on Nikon D500/500PF

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guitarman67

guitarman67

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I'm quite happy with the focus on my D500/500PF combo, but decided to follow Steve's guidelines for Auto fine tune...just to "try it out". I did this a couple of times and here are the results of the 12 amounts I got;
First time: -6 -1 -1 0 -5 -5 -1 -2 -2 +4 -6 -4 (average is therefore -2.7=-3)
Second time -1 -1 -1 +3 -1 +1-- +2 +1 +5 +6 +2 -2 (average is ?)

So...question 1: If there are +ve and -ve numbers in the same test...how do you work out the final average?
Question2: I read on another Nikon video that you should stop down 1 stop (ie for the 500PF select f6.3)...I used f5.6 as per Steve's video. Is this the case?
Question 3: What mode do you choose to run the test (manual, aperture priority, shutter priority)?
Question 4: Do you need to refocus (I use back button focus) each time you take a shot? I didn't in the two times shown above.

The testing was done indoors at a distance of around 10 metres (the maximum I could do indoors)

As I said, I feel my lens is fine as far as auto focus, but just wanted to try the fine tune to see if focus is improved. Cheers.
 
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Further testing: I took the camera/tripod outside and focused on a target (light fitting) on a brick wall across the road from my house. This time, with the camera in manual mode, I took a series of 7 shots (-3 -2 -1 0 +1+2 +3) as previous fine tune results seem to indicate around -2/-3 to be the sharpest.
When looking at the photos on the computer at 100% I would say that -2 was sharper, but only by a very small whisker. So...I guess leaving the camera at zero would be fine. Steve: would appreciate your feedback. Cheers.
 
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1) You add them up including minuses and take the average. In your last 7 shot example, -6 + +6 + 0 = 0 divided by 7 = zero :)
2) I think wide open is recommended
3) Doesn't matter
4) You need to defocus and then refocus for every shot.
 
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You are doing some thing seriously wrong here .. When I use auto fine tune I always get the same figure within 1.
You want a proper flat, contrasty target at about 20 yards or more (not a light fitting for gods sake,A light fitting sticks out from the wall so are you focused on the wall or the fitting ? Its FINE focus adjust !!) Re set the saved value to zero after each button push. The only majour problem I have had is not having AF-s on the REAR LCD. You cannot do any focus fine tune in manual as you are supposed to be micro adjusting the auto focus !!!
 
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" When I use auto fine tune I always get the same figure within 1 "

Well you're quite lucky then. I doesn't always go that way.
Yes, you should focus on a flat target (like Steve's) at a distance of about 25X (up to 50X) the focal length of the lens (25X = 12.5 meters for a 500mm). The focus target and the sensor plane should be parallel to each other. You CAN focus manually in Live View if you like, but Live View AF is OK, too. The camera is determining the difference between the two focusing points, so focusing manually in Live View is OK as long as you can do it critically.
 
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This is what I have learned about focus fine tune. I have to be very methodical in my testing approach. I have to see consistent results to be confident the adjustment will be beneficial. Testing outside is difficult due to environmental factors. I need a target that shows clearly the DOF so I can see the amount of front or back focusing. I like to confirm my adjustments using several testing methods.

Some years ago I purchased Reikan FoCal to do lens autofocus calibrations and it has been helpful. I can't say it has given me better results than other methods but it has helped me understand the focus fine tune process. FoCal runs in a tethered mode using a flat target. I takes a series of images at a fine tune setting of -20 and the software measures the image quality, it then takes a series of images at -15 and measures quality again, you repeat the process 5 units at a time until you reach +20. The software tries to fit a parabolic focus curve to the resulting measurements and the vertex of the parabola should be the focus fine tune adjustment value. When that point is determined it does more testing around that point to verify. If at any time it finds inconsistencies in the measured results it will give a warning or just stop testing.

I am not saying you need FoCal to do a good job of AF fine tune, just that you have to have an approach that gives you confidence that the changes you are making will improve the autofocus.
 
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For what’s is worth Dot -Tune seems to me to be a little more intuitive but to be honest I never tried it. I attached a link. It is. Very explicit explanation and well done . Check it out.
 
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guitarman67 said:
Further testing: I took the camera/tripod outside and focused on a target (light fitting) on a brick wall across the road from my house. This time, with the camera in manual mode, I took a series of 7 shots (-3 -2 -1 0 +1+2 +3) as previous fine tune results seem to indicate around -2/-3 to be the sharpest.
When looking at the photos on the computer at 100% I would say that -2 was sharper, but only by a very small whisker. So...I guess leaving the camera at zero would be fine. Steve: would appreciate your feedback. Cheers.
Click to expand...
Your first swings were far too wide - when you're at -6 and +6. Most of the time that's caused by poor support / technique when doing the test. Often, people overestimate their tripod's stability and you see those kinds of swings.

The second set is better and it does look like just leaving it at zero is a good choice. Most of the time AFFT is not needed and anymore I usually only advise it if you are actually seeing a consistent front or back focusing problem.

One misunderstanding with AFFT is that it makes the lens "sharper" and, naturally, people want the sharpest image they can get. However, that's not what it does. AFFT is to fix front or back focus and put the sharpness where the AF point is on the image and not in front of or in back of that location. If you don't notice consistent front or back focus, there's not an issue with AFFT (and it will only front or back - if you see both, it's technique).

Hope that helps :)
 
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Thanks everyone for the replies.
Pistnbroke: I should mention that my first attempts at AFFT were done indoors at a distance of 10 metres using Steve's target taped to a wall.

Steve: Sorry...should have made this clearer at the start. The outside ones were just photos taken of the fitting ( not auto fine tune) at different settings (-3 -2 -1 0 +1 +2 +3) and then checked at 100% on the computer to see if there was any difference in sharpness.
However, I may try the AFFT again indoors using the suggestions made here...but zero setting seems to be ok as you say. Cheers.
 
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I also use Dot Tune, made mention of the method here and what I used for a target.

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