40mm f/2 riddle

[sanmich]

I am scratching my head pretty good on this one, and would appreciate some help.
A friend of mine has a summicron-c that was in dire need of a relube.
We too it apart, cleaned, and remount everything.
It took us several trials to get the helicoids right.
The lens is now heavily front focusing.
My thought was that:
1- the Helicoid is the moving part, and communicates the distance to the camera. Since the infinity looks good in the camera RF, the Helicoids are ok.
2- the lens is front focusing, meaning the optical block is sitting too far in the focusing block.

trouble is: we released the optical block from the focusing block and there is nothing there. The adjustment ring is there, sitting as it seems it should, and no dirt or small object that could have be in the way of pushing the optics in place.

maybe No 1 is wrong?

we're really puzzled...

 

[Dan Daniel]

I don't know if this thread would help-

http://www.rangefinderforum.com/forums/showthread.php?t=129486

And there is a spacer ring. Discussed in this article, but not illustrated-
http://jumboprawn.net/jesse/cams/gear-profiles/leica-summicron-40mm.html

 

[Ronald M]

DAG charges double when he is delivered an item in pieces.

you are supposed to mark the helical with a witness mark before you take it apart. Now it is trial and error.

Back in the day, Leica warned the C lenses may not properly focus on M cameras.
True or not, I do not know. But it was official.

Look for a set screw or some other method of securing the optics in proper position.
Consider the helical may or may not be correct now.

 

[Mark C]

Was it focusing correctly before? If so, then the C lens issue probably isn't a problem. Sherry K agrees that these lenses can be a problem on M's, and explained the issue to me though I'm fuzzy on the details now. For some reason I was thinking the 40 was okay. I have seen problems with a 28.

I believe your thinking is correct on the helical. I take it you mean the rangefinder lines up correctly at the infinity mark.

So how about an element that is not seated properly. I had a lens come back from recoating by a very good repairer that had this issue and found an element not properly seated.

 

[Godfrey]

The issue with C lenses focusing on some M bodies has to do with the position of the lens' focusing cam and its implementation relative to the M bodies cam follower vs the CL/CLE cam follower. However, I've used both Summicron-C 40, M-Rokkor 40, and M-Rokkor 90 on my M4-2, M6TTL, and M9 without any focusing issues. So it's not an across the board incompatibility.

G

 

[maddoc]

The M-Rokkor has the M-standard focusing cam moving forwards or backwards depending on focus. The Summicron-C transfers focus via a skewed cam and it's position relative to the cam-follower has to be 100% exact to focus accurately. If you mount that cam in a rotated position all intermediate focus distances are off while infinity is still OK because infinity position is at the end of the cam slope.

 

[bonatto]

If it was working fine before, take it apart again, and try to insert the optical bloc in a different position. If you look at the helicoid threads at the edge the couples, you'll see there are quite a few options. Only one is correct.

 

[ferider]

Michael,

1) as is, is the lens sharp at infinity ? If yes, the problem is the cam/helicoid, if no, the problem is the collimation of the optical block.

2) check/adjust the Helicoid so that focus with the camera is correct at infinity, but more importantly at 1m (assuming the camera works). Then put in the optical block so that the aperture dot aligns with the infinity mark. Don't forget the spacer (if your lens has one). The measurements mentioned in post #2 tell you about optical block to helicoid distance.

Good luck,

Roland.

 

[sanmich]

Ok, first thing first, thank you all for the help.
I realized the helicoid could be wrong and infinity still ok.
Today we took it apart again, and got it right.
There are a few (2 maybe 3) possible threadings in the helicoids that seem ok (allow for a full focusing movement) but obviously only one is right.
It appears we had the wrong one, and that positioning the mechanism 1/3 of a circle of its right place (3 locking screws around) made it look right for the RF connection, while the optical block was not in place.
everything looks good now!