Detecting Back Focus

rpsawin · Jun 4, 2020

I have three Konica Hexanon M lenses (28/2.8. 35/2 50/2). and would appreciate any info on how to detect back focusing. I would like to use these lenses on both a digital and various film Leica bodies. Thanks in advance for your help.

Best regards,

Bob

ic-racer · Jun 4, 2020

I'd start by collimating the lenses (that is set the infinity stop of each lens to match the film plane at infinity). Then work on synchronization of lens focus focal point to the rangefinder.

grain elevator · Jun 4, 2020

You have a digital Leica? Just see if your pics are in focus or back focused, what's the problem? Easiest is to photograph a yard stick at an angle.

nosmok · Jun 4, 2020

I just put a piece or 2 of Scotch 'Magic' Transparent tape across the film opening of a film camera (and whatever rollers are nearby) and check focus, starting at infinity. The adhesive side of the tape acts like a ground glass. If you have confidence in your digital rigs, you could use them as the standard focus check.

BSP · Jun 4, 2020

nosmok said:
I just put a piece or 2 of Scotch 'Magic' Transparent tape across the film opening of a film camera (and whatever rollers are nearby) and check focus, starting at infinity. The adhesive side of the tape acts like a ground glass.

This is genius!

ic-racer · Jun 4, 2020

Usually the tape is on the lens side of a microscope slide or other piece of optically flat glass.

nosmok · Jun 5, 2020

ic-racer said:
Usually the tape is on the lens side of a microscope slide or other piece of optically flat glass.

This is certainly true, however my feeling is: since roll film is flexible as is tape, it's a good representation of what's going on with the camera/lens/film system. Any consistent anomalies (1 side being out of focus all the time, say) could be checked with a glass standard to see if the lens is bonked, or such.

grain elevator · Jun 5, 2020

nosmok said:
This is certainly true, however my feeling is: since roll film is flexible as is tape, it's a good representation of what's going on with the camera/lens/film system. Any consistent anomalies (1 side being out of focus all the time, say) could be checked with a glass standard to see if the lens is bonked, or such.

I'm wary of tape, too. It's actually more flexible than film, and film is even more rigid by virtue of being a larger strip, plus there's a pressure plate so it can't move backwards at all. A matte screen or piece of glass isn't hard to come by... Anyway, apparently the OP has a digital Leica, that should do nicely.

Detecting Back Focus

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