How to shim LTM lense ( Nikkor 50/1.4)

[bluelight]

Hello,

I have a Nikkor 50 1.4 LTM and after I sent it for collimation, it is now back focusing. Infinity seems to be fine and at 1 M, it is back focused for about 2 inches. I checked the lens in R-D1 and M4 and the back focusing is consistent.

I contacted the camera repairman and he said that it should not be changed as it was set correctly.

I trust my camera body and off I went to borrow a lens spanner. I opened up the lens and found a copper ring shim. ( I was lucky enough to be able to put it back together).

My question is by how much I much add to the shim and how to add additonal thickness to it?

Thanks

[hans voralberg]

Fire a PM to Brian :P

[Brian Sweeney]

You have an RD-1 for quick tests, so you are lucky.

When a lens focusses behind what the RF indicates, the optics module needs to be moved out a little from the film plane. The focus on the Nikkor (and most Sonnars) shifts a little bit as you change F-Stop. BUT- The 2" error is to big to be accounted for by focus shift.

I would start with ~0.1mm added to the shim. If you do not have extra shims, you might try starting with some aluminum foil. I do not have any shims for the Nikkor.

[bluelight]

Thanks hans/Brian.

We try to create some shim from platistic foil to see if it fits. I just hope that after shimming, my infinity is still on....

[Brian Sweeney]

If the close focus is good, and infinity is far off- something is wrong with the spacing of the elements. I suspect you'll find infinity is just fine after shimming to get the close focus correct. IF NOT- report back.

[bluelight]

Thanks Brian,

Will take a test shot at infinity first and try the shimming. Will report soon.....

[leica M2 fan]

Originally Posted by Brian Sweeney

You have an RD-1 for quick tests, so you are lucky.

When a lens focusses behind what the RF indicates, the optics module needs to be moved out a little from the film plane. The focus on the Nikkor (and most Sonnars) shifts a little bit as you change F-Stop. BUT- The 2" error is to big to be accounted for by focus shift.

I would start with ~0.1mm added to the shim. If you do not have extra shims, you might try starting with some aluminum foil. I do not have any shims for the Nikkor.

Am I understanding this correctly? If the lens focuses behind the indicated RF do you need to "move " the optics module "out" from the film plane toward the front of the lens by shimming? And the reverse if the lens is front focusing? Thanks for your reply .

[ferider]

Yes, Tony. Making the lens longer moves the plane of focus towards you.

Roland.

[leica M2 fan]

I was not sure I was understanding it, I've got it now! Thanks again.

[Brian Sweeney]

Originally Posted by leica M2 fan

Am I understanding this correctly? If the lens focuses behind the indicated RF do you need to "move " the optics module "out" from the film plane toward the front of the lens by shimming? And the reverse if the lens is front focusing? Thanks for your reply .

When you focus a lens at infinity, it is at it's closest point to the film. It is farthest from the film when it is focussed close-up. So if the RF indicates a point of focus, and the actual focus is beyond what is indicated, it means the optics are closer to the film than what the RF expects. SO the optics need to be moved out with respect to the RF cam in the focus mount. Shimming is the most common way to do this.

[leica M2 fan]

Makes absolute sense, thanks for your explanation.