Nikkor-P 10.5cm f2.5 LTM cam adjustment?

[shawn]

I have a Nikkor-P 10.5cm f2.5 in LTM. At the infinity stop the optical focus is spot on, however the RF image is quite a bit off.

On closer objects the lens is back focused compared to the RF.

Is the RF cam adjustable on this lens? And if so any good guides on how to do it?

Thanks,

Shawn

 

[dourbalistar]

I think Richard Haw's repair guide is for the Nikon S-mount version, but you might be able to glean some information for the LTM version:
https://richardhaw.com/2017/06/18/repair-rf-nikkor-p-105mm-f2-5/

 

[Sonnar Brian]

What camera are you using the lens on? Make sure that the Cam of the lens is making good contact with the Cam follower of the camera. If you are using an M-Mount adapter, make sure the RF cam is coming up to the cut-out on the adapter.

Assuming the cam is making good contact: the easiest way to correct for back-focus is to build up the RF cam by using tape. I use copper tape. Depends on how far things are off, but I've not had to use more than 1 layer of 3M copper tape. I've done this for a Nikkor 13.5cm F3.5.

 

[shawn]

Thanks, was just looking through that. It looks like the S mount and LTM mount are fairly different or maybe Nikon changed it over time. Mine is late production for LTM. (serial number 920xxx)

Haven't taken it apart yet but looking through the rear the RF actuator rides on a traditional cam on a helical, I don't see that in his shots. It also looks like the rear of the lens is somewhat different as the LTM has 4 large screws near the mount, 2 for the tripod mount and two on the opposite side.

Shawn

 

[shawn]

What camera are you using the lens on? Make sure that the Cam of the lens is making good contact with the Cam follower of the camera. If you are using an M-Mount adapter, make sure the RF cam is coming up to the cut-out on the adapter.

Assuming the cam is making good contact: the easiest way to correct for back-focus is to build up the RF cam by using tape. I use copper tape. Depends on how far things are off, but I've not had to use more than 1 layer of 3M copper tape. I've done this for a Nikkor 13.5cm F3.5.

I tested optically on a M240, I could test optically on my Tower 45 too but I doubt I'd see anything different.

Tested the RF on the M240 and a IIIG. The RF is off about the same on both cameras, the image never comes together at infinity so the cam needs to be deeper into the camera.

Tape on the cam would certainly be easy. Any concerns with it coming free over time? Pretty sure I have some 3m copper tape.

Thanks,

Shawn

 

[Phil_F_NM]

Since your cam is off, how are the index marks of the lens itself? How are they oriented according to the camera body? I ask this because if the cam is off significantly, the lens helicoid assembly has been taken apart and reassembled incorrectly.

Phil Forrest

 

[Sonnar Brian]

I've had the same strips of copper tape on some of my lenses for over 10 years, use them on the M8, M9, and M Monochrom.

 

[shawn]

Since your cam is off, how are the index marks of the lens itself? How are they oriented according to the camera body? I ask this because if the cam is off significantly, the lens helicoid assembly has been taken apart and reassembled incorrectly.

Phil Forrest

On a LTM body the tripod mount is exactly down and the DOF index marks are centered at about 3 oclock. Basically the same place as my Nikkor HC 5cm f2, that one was CLA'd by YYE.

Shawn

 

[shawn]

I've had the same strips of copper tape on some of my lenses for over 10 years, use them on the M8, M9, and M Monochrom.

Nice, I'll give it a try.

Shawn

 

[Phil_F_NM]

On a LTM body the tripod mount is exactly down and the DOF index marks are centered at about 3 oclock. Basically the same place as my Nikkor HC 5cm f2, that one was CLA'd by YYE.

Shawn

The tripod mounts of some of these lenses can be adjusted about 1 cm. Usually, the index marks of Nikon LTM lenses point roughly to the RF window, about 1:30-2:00, looking at the camera from the front. If your indexes are 90 degrees right, at 3:00, either your lenses are both off or your camera flange may have been removed, too many shims added, then put back on 90 degrees off.

Phil Forrest

 

[shawn]

The tripod mounts of some of these lenses can be adjusted about 1 cm. Usually, the index marks of Nikon LTM lenses point roughly to the RF window, about 1:30-2:00, looking at the camera from the front. If your indexes are 90 degrees right, at 3:00, either your lenses are both off or your camera flange may have been removed, too many shims added, then put back on 90 degrees off.

Phil Forrest

Looking again it is pretty close to pointing at the viewfinder window. The tripod mount isn't quite perfect on the M240 but I'm sure that is the adapter as it is fine on any of my screw mount bodies.

Shawn

 

[shawn]

Tried the copper tape, it took two pieces to correct for the back focus. Infinity looks like it aligning just about right and that is with a 1.25 magnifier on it to check carefully.

Shawn