lens cam lenght??

[Lukino]

Hi, I've just boght a Zorki. Cheap ebay auction, over a month shipping time, in the end is here. Yesterday I've made a deep clean of it, including the inside of vf that was so dirt, no lubing since it seems to work just fine. RF alignment vas off since the arrival, so I've fixed it for infinity and close focus, lot of time but no big deal. Then, surprise!!!
😱
I've bought 2 lenses with the camera, an industar 50 (it was included) and a faster jupiter 8. I've aligned the camera with the industar, then cheked the jupiter "just to"... and they focus different! 😕 I've cheked the lens' cam excursion at one meter (from the lens scale), and there is about 0,1mm of difference!! :bang: It also seems to be a little difference at infinity too, in the order of 0,05mm but I cannot see differences in the VF, that are very visible at 1m. Curiosly, 1m excursion with the industar seems to match the minimum focus distance one of the jupiter.

Can someone help me fix this, or at least find what lens is the correct one without wasting film?
Can someone measure the cam excursion of their working lenses at 1m and infinity?
10x

 

[Sonnar Brian]

That may not help you- many of the FSU lenses, especially the faster ones, sometimes require "fine-tuning" with a particular camera. The optics module needs to be "shimmed".

Shoot a test roll and judge the results. If the J-8 focus is off, there is a variable stand-off ring that can be adjusted to correct the focus on your camera.

 

[Nickfed]

FWIW, and as best I can read on a vernier, my I-50 has a flange to cam distance of 7.5mm at infinity, and moves forward 3.04mm when the scale is set to 1m. The latter figure hardly matches the theory. My collapsible has a flange to cam distance of 7.72mm and moves forward 2.92mm.

Assuming your lens has a focal length of 52.3mm, the "Contax Standard" attributed to FSU lenses, it should move forward 2.886mm from its infinity position when focussed on 1m. For a given scale length, i.e. amount of rotation, this movement is determined, for better or worse, by the focussing thread of the lens. It has nothing to do with shims, or anything, just the thread.

You could conceivably adjust one lens so that the projection is the same as another at either 1m or infinity, but if the forward movement is different, you are not going to fix things at the other end and that chance of making the situation worse is pretty good.

So the first thing to do is to check the accuracy of your measurements. Your post implies a different "error" at each end of the scale. You should expect the "error" to be the same at both ends of the movement. If it isn't, I guess you can conclude that the threads are different and that may be a strong hint about the significance of all this - and also what you can do about it.

The next thing to do is to determine how necessary the adjustment actually might be.

Assuming the lens with the least projection is actually focussed on infinity, a 0.5mm discrepancy means that the lens in relative error will actually be focussed at about 54m when set to infinity on the rangefinder, and you will be struggling to find any difference. At the near distance it will be focussed at 983mm, and much the same can be said for that.

Just by way of comparison, my Leica lens has a flange to cam distance of 7.8mm and moves 3.1mm, which is quite funny, considering its focal length of, ostensibly, 51.6mm. I guess this tends to point out the relevance of all this.

 

[Lukino]

Thanks Nickfed, probably my compulsive fixing syndrome will remain unsatisfied... So I'll set alignment of the Zorki with the Jupiter, and try a test roll. I just hope this lens will work fine, if it will I'll probably never use the industar, so no big deal until I can afford some other russian crazyness. Too bad I'm so out of money now...

 

[Lukino]

So, after having surrendered to aligning my zorki to only one lens, I was procrastinating wihile toying with the Jupiter... what the heck! It was loose!
😱
I've managed to dismantle it (catched the front lens element just before it felt on the ground), removed the lens assembly from the focusing unit, cleaned the MANY debris I've found inside, thightened the many loose little screw, put everyting togheter again...

And now close focus matches the industar! Foggy night outside, cannot test the infinity, but probably ok too.
Never surrender! 😀

 

[Lukino]

checked today: the focus of the two lenses mathces perfectly, both at 1m and at infinity.
I also realized that I didn't dismatled the focus unit, only cleaned between it and the lens unit, so it sound like pointless, but works. 😕