a6k Loc: Detroit & Sanibel

This came up originally in my previous thread when "Imagemeister" asked me if had done it on my Minolta 500/8 Reflex lens which is an A mount lens that I use with a LA-EA4 adapter on my 𝜶6500. At that time I thought it did not need it. I reconsidered and looked for how to do it. I'm glad he asked the question and I'm now happy with the outcome. Thanks.

I found a terrific video on the internet that demonstrated using a simple, sharp target and simply interating through the possible settings then looking at the results to see which one was best. That is a lot simpler than targets at 45 degrees and expensive specialty targets. His approach was to try a large adjustment at each end of the range (minus to zero to plus). I think I have improved it. He goes back and forth; I started at one end.

BTW, I could not find anywhere in my EXIF, even using "Exiftool" that says what the lens adjustment was. I had to simply go Old School and take paper/pencil notes. If anyone can help me with finding that information in Exiftool I'd be grateful.

I started at -5 and took a series of exposures, each one closer to zero. As it happens, I got lucky and I chose the right end of the range and my -5 was far enough from zero that I did not need to go further. My improvement was simply to start at one end so that I could see which direction to go. You could start at zero and go toward either plus or minus and it would be equally good.

My lens on my camera only needs a -2 to be the best that it can be. Perhaps if the increments were smaller I could do even better, but I've now done what I can with my actual gear.

I used a resolution target from Edmund Scientific that I downloaded. But really, anything will work. I did not print the target. Rather, I used it on my 27" 4K monitor. I set the monitor for B&W and made it as bright as I could. I reviewed the shots in FastRawViewer. You could use any software that allows pixel peeping but FRV makes it convenient because once you have zoomed in to 100% or even more, then it will apply that magnification to all the images in the current folder. All I had to to was move from one image to the next until it was sharpest. I knew when I got there because the next image was less sharp.

This was so easy I just had to "share" it.

If you want to find the original video, look for "Gary Reed Unfrequented World" and the particular video is "How to micro adjust lenses". There are probably many good videos to be found but that is the one I saw and liked.

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Did you put your monitor at one end of a long hallway to get a reasonable distance for a 500mm ? Or put it in a window and shoot from across the road ? Etc etc ?

a6k Loc: Detroit & Sanibel

It was probably 13' or maybe a little more. The zoom lenses have a different problem but this is a fixed length, fixed aperture lens.

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As you may already know, AF tweaking only targets and attempts to perfect focus for just one distance. Other focus distances might be equally improved ... or “less equally” improved. IOW I was expecting that you tweaked it for the most likely distance for its use. That is why I inquired about how you used a monitor as a test target, becuz I was expecting a 75 to 200 ft distance.

You may be lucky. A 13 ft adjustment might prove equally successful for all other distances. But that needs to be confirmed. It’s not to be assumed.

a6k Loc: Detroit & Sanibel

I don't know if you are correct about this. I am sure it makes a difference with a zoom lens but I'm not sure about this kind of lens. But since reality always trumps theory, I took the same series with a target that is about 500' away. The result was that -2 was still best but if I could have tried -1.5 that might have been better. Sadly, the camera won't do that. The good news is that I can leave it at -2 for the entire range of distances at which I would use this lens (wildlife and birds).

Thanks for the tip.

This is a screen capture of zero, -1 and -2. The file names have been tweaked for clarity. These are 1:1 on my 4K monitor, showing in Preview on my Mac. I focused on the triangle shaped brace for all 3. The easiest place to compare is the vertical line at the right edge of the square brace behind the triangle. You can also look at the edge of the screening where it rolls around the rubber gasket (the left one). Also, the end of the eye bolt where it protrudes through the nut is useful.

(Download)

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I find the threads on the eyebolt are defined best at -1, and not as distinctly identifiable as threads in the other two images. Also the hex faces of the lock nuts have sharper edges at -1.

Whatever. IIRC it’s a screwdriver lens so it may vary more at each new focus than than the differences seen between your posted examples. IOW, not much to be gained from further eye strain.

imagemeister Loc: mid east Florida

FWIW, the MFA for 500 Reflex on my A99 is also -2 ......
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