CV 40 cam adjustment?

[mto'brien]

Hi Brian (and all),
Sorry if I'm posting in the wrong place or if this has been asked before, but, you are the mad scientist.

I just got an M8 and tested these lenses on it:
CV 40
CV 35 1.7
CV 75 2.5
CV 15
CV 25
Summarit
Summar

All are spot on except the 40. It won't close focus correctly wide open. I'm not talking about the focus shift issue with some copies, I'm talking it's a hair off, only at 1.4. Or rather, it's only noticeable at 1.4. I have been cheating the RF patch just a bit to the right (toward infinity) of the focus point on the subject and it's dead sharp. I don't want to do that forever, and I dont want to adjust my RF for just one lens...so:

Is there a way to DIY adjust the focus cam on the lens? If I'm not mistaken, a shim wouldn't do it because the cam is protruding too far?

Any help would be greatly appreciated, thanks.

[Brian Sweeney]

I have never handled one of these, let alone take one apart.

If the error is only when used close-up, but correct for all other distances: the focal length might be slightly off. That means in internal adjustment to the optics.

If it is off at all distances: could be the shim, or the double-helical is slightly off.

This sounds more like a job for a camera repairman, or DIY- depending on comfort level.

Does anyone else have experience with this lens?

[Ronald M]

If infinity is correct and the other lenses work close and far, then it is a problem with the lens focus helicals moving the optics the wrong amount.

If infinity is off, then recollumnation is in order. Unless you have a supply of thicker, thinner shims, I would leave this to someone else.

These are not precision lenses and you get what you pay for. If you saw the insides compared to Leica, you would see what I mean.

[mto'brien]

Thanks for the replies fellas. I'm going to leave this one alone...

[mto'brien]

Well, I decided to not leave it alone and figured it out, but...
the focus was off enough to where for close up wide open portraits, I would have to focus roughly on the nose (depending on nose size) to get the eyes in focus. Total pain. So, I cut some shims to fit around the rear element and it turns out the focus was off by the thickness of 2 sheets of 20# paper (about .2mm? a guess). Focuses great at near and infinity now.

So, my new question: is it OK to just go with the paper shims, or is there a source for metal shims in various thicknesses? The paper works fine, but I thought you (all) would know best. Thanks.

[Brian Sweeney]

Paper shims work quite well, and if it working now- I would use it.

Kitchen Aluminum foil is about 0.07mm. So- three layers would be ~0.2mm.

Question: Did you move the entire optics module out by 0.2mm?

Or did you unscrew the rear optics module, use the shims so that it moved out 0.mm from the front optics group?

The first: moving the entire optics module out leaves the focal length the same.

The Seconde Method, increasing the separation between front and rear groups Increases the Focal Length. I've done both methods to correct focus problems.

[mto'brien]

I didn't open the lens, I put the shims directly onto the cam around the rear element to shim the coupling. The lens now focuses perfectly on my M8 and I can take the shims out when I mount it on my film body which doesn't need them. I'm happy with the solution, but I wonder if I should use a different material because I fear the possibility of a shim coming loose/tearing and mucking up the works. I'm going to try foil so that I could form it around the cam tightly. What do you think?

[ferider]

Matt, the attached pictures show you a disassembled Nokton 35/1.4.

You can adjust RF coupling via (5). The 40/1.4 is built similarly (I did have one apart but didn't take photos), but easier to disassemble, since it doesn't have the rear element (1) covering the rear span ring (2). All you need is a lens spanner and your 40 will come apart and give you access to RF coupling screws and shims (4).

Hope this helps.

Roland.

[mto'brien]

Roland, Thanks! That does help.

[Frankie]

Originally Posted by Brian Sweeney

Paper shims work quite well, and if it working now- I would use it.

Kitchen Aluminum foil is about 0.07mm. So- three layers would be ~0.2mm.

Come on, Brian...paper and aluminium foil?

You can buy all kinds of shims and shim stocks here:
http://www.mcmaster.com. And I have posted this link in the first sticky at the start of the Mad Scientist sub-forum.

Just type in "shims" at the web site search window.

They even have ones that is like a very large washer (ID at 30 or 40mm) at 0.1mm thickness and up...brass, stainless...

McMaster-Carr was my main supplier of parts when I retrofitted Wild-Heerbrugg (renamed Leica in 1991) photogrammetric instruments. Their quarterly yellow covered catalog was thicker than a NY city phone book.

[Brian Sweeney]

Having a supply of shim material and shims is necessary for a repairshop, nice to have around. But for the one-time, need to fix a lens, aluminum foil and paper work.

I'm lucky to have a machine shop at work with supplies.

And- I would not use paper at the back of the Cam, especially on an M8. I've used copper tape on the back of a cam.

[paulinventome]

Originally Posted by ferider

Matt, the attached pictures show you a disassembled Nokton 35/1.4.

You can adjust RF coupling via (5). The 40/1.4 is built similarly (I did have one apart but didn't take photos), but easier to disassemble, since it doesn't have the rear element (1) covering the rear span ring (2). All you need is a lens spanner and your 40 will come apart and give you access to RF coupling screws and shims (4).

Hope this helps.

Roland.

Roland,

I have a CV 35/1.4 and this is really useful. When you mention the coupling screws do you mean there's a way to get this to focus closer than the minimum focus distance? (I don't need rangefinder coupling as i'm on a NEX)

cheers
paul