Jupiter-12 collimation

V

varjag

Guest
Yesterday I checked the working distance of my J-12 (black, Kiev mount), and sure enough it was off.

At 0.9m distance it actually focuses when turned to between 1.3-1.5m marks: pretty big barrel throw. I know there are people here who have experience collimating Jupiters, so hope for some help.

With such misalignment, should I add to the shim thickness or substract?

Any guesstimate on how much needs to be added (I plan to add up with kitchen aluminium foil)?

Why is it necessary to check both at infinity and close range, would it affect the adjustment?
 
Substract thickness to make the actual focus move out toward 1.3 meters.

Assuming the helical pitch is constant (if it were not, it would bind at one end), an adjustment at one end of the focus range should affect the focus at the end as well.

You might want to consult a DOF table for the 35mm lens and see if the difference in focus is actually significant for that focal length lens. My experience with Soviet-era equipment is that there is a lot of tolerance in working precision, but that most of the time it makes little practical difference in the outcome.

-Paul
 
Thanks Paul!

So should I actually grind the spacer a bit?

Regarding the focus difference, I can clearly see the excessive softness of the test target at 0.9m position compared to that when helical turned to 1.4m, and wide open shots indeed exhibit the softness.
 
Eugene:

I am probably not the best person to consult about physically altering lenses. I have had similar issues with a Jupiter-8, and I elected to modify the camera (a Fed-2 instead). The camera body was less expensive and the procedure (grinding a flange) had a better chance of success.

Sovet bodies are so inexpensive (close to the cost of a high quality lenscap) that I elected to modify and dedicate a body to the lens.

Do you really shoot much with the Jupiter-12 at distances close to 1 meter at full open aperture? The consequence of making the lens work absolutely correctly at 0.9 meter might be to throw off the infinity focus.

-Paul
 
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