Just how much does the lens mount do?

[Chuck A]

I have been contemplating doing the modification on my 40mm M-Rokkor to bring up the 35mm frames. I have done some tests and find that the 35mm frames are a perfect match for the 40mm lens at the medium to longer distances. I am reluctant to modify the lensmount though. Mostly for resale value.

Then it occurred to me. Can't the lensmount be changed with one from a 35mm lens? I am sure that there are lensmounts available from broken 35mm lenses or does the lens mount have to be matched to the lens. From what I can tell the lens mount holds the lens and cues the correct framelines.

When I look at my 40 and 90 the lensmounts look interchangable. (although I haven't tried to change them) But they are both M-Rokkor lenses. Can anyone check to see if the screws line up on the Leica M mount with the screws from the M-Rokkor mount?

So, is this possible or am I just being silly.

 

[Kim Coxon]

Although the lens mounts might look identical, I would check with a pro camera repairer first. The tolerance for the film plane/flange is very tight. By changing the lens mount you may be altering this which will affect the focus registration and thus the accuracy of the focus. Providing the mounts are the same and you get the collimation checked afterwards, I can't see a problem but getting the collimation done on an expensive piece of glass needs a proper rig. You will be able to get it fairly close using a good ground glass screen and high quality lupe but it will need a proper rig to check it is accurate to the couple of thou needed for best performance.

Kim

 

[FrankS]

Just file the existing mount if you want to automatically bring up the 35mm framelines. Your was an interesting possible solution, but this is the easiest and proven solution. The only negative about this modification is if you ever plan to use this lens on a CLE. It would then bring up the 28 framelines on that camera, I believe.

 

[Chuck A]

Frank,

You are right that filing the mount is the easiest solution. I just thought that this would hurt the resale value if I ever want to sell it down the road. It really only affects the CLE so maybe not.

 

[Andy Aitken]

I'd say its far, far less risky to file a tiny bit of metal of the mount than to go messing with changing the mounts. Don't worry about the resale value - I doubt you'll ever want to part with your 40mm f2

 

[Xmas]

Chuck
If you can procure a parts lens and salvage the mount you only need to micrometer the mount is the same to better than tolerance. You can grind the scrap mount and swap it back for resale, then sell the scrap lens on.
Noel

 

[Dougg]

I don't like the idea of filing on the lens, so I admire the lens mount idea. My CLE is my fav 35mm RF, so not much interest here in modifying the lens. But I have used one of my 40's on my M2, and accomplished the frameline change with a rubber band. Yes, I actually tried it, and it works because of the shape of the frame selector lever on the M2... I stretch a rubber band around the end of the frame selector and the other end loops around the left-side strap lug. The tension keeps the 35 frame selected. This might not work so well on later M bodies having a lever with a straight-sided shape.

 

[Palaeoboy]

The mount on the 40mm CLE Rokkor forms part of the focusing helix. It therefore is not interchangable with any other mount even the other Rokkor lenses.

As has been mentioned if you file the lens it will no longer be usable on a CLE as 35mm lenses dont bring up any framelines on a CLE although the 28mm framelines are always visible.

If you do attempt to modify the lens I do have some spare mounts in my box of new spare parts if you decide to ever return it back to original although that may not be worth it as there should be a buyer for a modified lens.

 

[Chuck A]

Thanks for the info. I sent a PM to Palaeoboy about a spare mount.

 

[Andrew3511]

The modification to the mount is very small. The difference between the size of lug that brings up the 3 different frames is about 1.5mm per frame. I just filed away the bayonet lug very gradually until initially the 50 and 35mm frames sort of appeared together and then eventually the 35mm appeared alone. I test-fitted the lens about half a dozen times during the process and protected the optics and mount with masking tape. My main problem was in fact trying to remove the adhesive from the masking tape, so I wouldn't recommend this one, just a bit of cloth and a steady hand on the file.

 

[Xmas]

Hey I need an elastic band. Does it have a Leitz five digit code?

magic idea

Noel.

 

[Justin Low]

A small piece of 1mm thick card works wonders too. Just slip it between the body and the lever, and it'll provide enough resistance to make your selection stay.

 

[Chuck A]

A small piece of 1mm thick card works wonders too. Just slip it between the body and the lever, and it'll provide enough resistance to make your selection stay.

Great idea. I am currently using a toothpick.