Loose aperture ring in hybrid CZJ 50/2

[like2fiddle]

Last year, with much help from Brian, I did my first lens project: a pre-war CZJ 50/2 to J-8 ltm. I was in such a hurry to use the lens that I let a little detail go unfinished. In order to use the lens and have the aperture numbers line up with the mark on the lens barrel, I had to leave the lens itself slightly loose - unscrewed. It's worked fine that way as long as I'm careful AND use a metered camera. Now I want to get it right and tighten the thing the way it should be so that I can use it on a meterless camera and know for sure what the aperture opening is. Is it a matter of adding shims? The focus seems pretty good right now and I don't want to start all over again with that.

[Brian]

How much of a turn does the lens require to tighten? 1/4th turn, 1/2, etc? You need to add a thickness to the shim equal to the (thread_size * fraction_of_a_turn). The thread size of the 5cm f2 Sonnar is 0.5mm per full turn (just measured 4.5mm for 9 turns).

I try to get the F2 lens within 0.05mm or better. ALSO: remember that the SOnnar can be adjusted using the variable stand-off ring that the Shim rests on. Use that for really fine tuning.

Once the lens is shimmed, you will probably need to loosen the 3 set screws for the aperture ring, make a few new taps for them, and retighten.

[like2fiddle]

Thanks for your reply Brian. I don't think it will take too much of an adjustment, it's off by about 6 or 7 mm; in other words, when the lens is fully stopped down, the green dot/marker is on "11" on the aperture ring instead of "22". I'm thinking adjusting the variable stand-off ring and not fooling with shims.

[Brian]

That would be the best option- and it is well within range. When you find the correct spot, you will probably need to tap out a spot for the set screw to rest. You need to make sure the ring is not "thrown to one side" when you tighten it back down. SO: head of screw must clear the thread, and it must not be so tight that the ring is off center. Otherwise, the optics module will not go in properly.

Ask me how I know...

[like2fiddle]

Ok, thanks Brian. I have to work the weekend so I have the next couple of days off - hopefully I"ll be able to play with the lens some time tomorrow or Friday. I don't remember - do I want to adjust the variable stand-off ring clockwise or counterclockwise in this case?

[Brian]

To make the optics farther out, you have to unscrew the variable ring. Back it out the same amount that the lens needs to screw into the mount.