Zorki 4 rangefinder calibration woes.

[hamradio]

I've got a '62 Zorki 4 that I'm ripping my hair out over. Registration distance is spot on at 28.8mm with a caliper and infinity looks quite nice with an old slr focusing screen taped in place over the film plane. Closer ranges had always been off by about a foot.

I decided to tackle this tonight. I set up tripod and gridded paper on a wall 1m away, mounted a Jupiter 8, and continually compared the J8's focus on the focusing screen against the RF as I adjusted the little tab on the end of the RF arm. After I got it spot on, I mounted an I61 to the camera to double check against another lens. Perfect.

I moved the tripod around and focused on a subject about 2.5m away. The RF was about 6" off of the image on the ground glass. I mounted the J8 and got the exact same thing.

I'm kind of stuck here. Any ideas why there would be a discrepancy between 2.5m and 1m?

 

[colyn]

1m focus is set by turning the rf cam. Infinity focus is set by the screw.

You may have to play with both to get both infinity and 1m set properly..

 

[wolves3012]

As colyn says, there are two adjusters and by moving the RF sensor tip you will have upset the infinity setting. There is a sticky thread on how to adjust your RF. To save repeating what's in it, I'll just suggest you read it. If you have adjusted it to be correct at both ends, then the in-betweens will also be correct.

 

[renek337]

This may help.
http://jay.fedka.com/index_files/Page422.htm

 

[hamradio]

Ah, excellent. Thank you very much, all! Looks like I have an hour or two of trial-and-error ahead of me.

 

[Crazy Fedya]

I think it also might have something to do with famous Sonnar focus shift.

 

[Jonathan]

Sonnar shift was noted by Zeiss in the thirties, so it is not a new phenomom.
Regards, Jon

 

[Jonathan]

Should have said, phenomenom

 

[mburns]

Your measurement is so precise that it reveals mathematical imperfections in the design of most rangefinders. My Yashica GSN also has this 6" disagreement, showing 9.5' at a measured 9' from the film plane. This camera is properly adjusted at 5' and infinity, just as is possible with the two adjustments available.

 

[hamradio]

A little update: after a ton of messing around, I got it spot on. I61 checks out perfect at close range, mid ranges, and infinity. The J8 is perfect at infinity and mid, and just a hair off at 1m; maybe an inch. Not sure if this is due to it being a little faster than the I61, or due to the sonnar focus shift. I doubt I'll notice anything adverse from the test roll. I'm quite happy.

Thanks all!