LTM Nikkor 5cm f1.4 & f2 close focus coupling modification

[jonmanjiro]

Those who own an LTM Nikkor 5cm lens will know that the lens itself can focus down to about 0.45m (1.5 feet) but focus coupling disengages between 1m (3.3 feet) and 0.45m, which makes focusing closer than 1m guess work unless you have live view.

Here's how to modify the lens mount to enable focus coupling between 1m (3.3 feet) and the minimum focus coupling distance of a standard M-mount rangefinder camera (usually around 0.65-0.70m or just over 2 feet).

Below on the left on the camera is a late s/n Nikkor-S 5cm 1:1.4 that served as the model in this short write up, and on the right is a late s/n Nikkor-H 5cm 1:2 that I modified a while ago. Both the LTM Nikkor-S 50/1.4 and LTM Nikkor-H 50/2 can be modified for close focus coupling.

** Note **

Early s/n focus helicals are assembled differently from late s/n focus helicals. The following is for late s/n helicals. See further down the thread for info on early s/n helicals.

 

[jonmanjiro]

First, loosen and remove the retainer ring on the rear of the lens.

After it is removed, the lens disassembles into the following four pieces.

 

[jonmanjiro]

Next, remove the three screws that hold the focus helical together. The first screw is shown below, and the other two are at equal distances around the circumference of the focus helical. Note that earlier version lenses are designed a bit differently and don't have these screws. I'll add a section about the earlier lenses when I have an opportunity to modify one.

When the screws are removed, the focus helical disassembles as follows:
Take care not to lose the 1m bump ball bearing (or remove it if you don't want the bump).

 

[jonmanjiro]

Next, you can unscrew the three pieces that comprise the focus helical. Make sure to mark the parts so you can reassemble them correctly.

The disassembled focus helical looks like this:

 

[jonmanjiro]

Next, screw part A onto an LTM-M adapter and mark where the cut needs to be made.

Time for some dremel work. The end result should look something like this:

The end goal is this:

 

[jonmanjiro]

Clean, lubricate, and reassemble the focus helical, and reinstall the optical cell and spacer shim. If all goes smoothly, you will have a feshly CLA'd smooth focusing lens that focus couples down to the minimum focus coupling distance of your camera.

 

[BillBingham2]

Wow!

B2 (;->

 

[MikeL]

Super, Jon!

 

[Robert Lai]

For those of us in the USA, Don Goldberg can perform this modification for you for minimal cost, along with the CLA of your lens. He does this on a milling machine, so that the cut is perfect, and very professionally done.

 

[ferider]

A nice reminder, Jon, showing how this can be done. See also my original thread (https://www.rangefinderforum.com/forums/showthread.php?t=56962) from March 2008, documenting this mod for the first time:

Note that you don't need to take the helix apart for the mod, just put it on close focus and cover the inside of the helix with tape to keep the filing "shrapnel" out.

Also note that the helix might be assembled differently, depending on the age of the lens (confirmed by Rotoloni):

Roland.

 

[jonmanjiro]

Wow!

B2 (;->

Super, Jon!

Thanks 🙂

For those of us in the USA, Don Goldberg can perform this modification for you for minimal cost, along with the CLA of your lens. He does this on a milling machine, so that the cut is perfect, and very professionally done.

Robert, that's a great option for those who don't want to undertake the work themselves. Do you know how much Don charges?

A nice reminder, Jon, showing how this can be done. See also my original thread (https://www.rangefinderforum.com/forums/showthread.php?t=56962) from March 2008, documenting this mod for the first time:

Wow that's a blast from the past, Roland. Thanks for linking. I think I was lurking exclusively in the Nikon RF forum back in March 2008, so its my first time to see the thread. I do remember seeing another thread some years back where several people showed their hacked mounts (including someone who had two goes at hacking the mount to get the right position 😱), and I think you posted some photos there as well.

Note that you don't need to take the helix apart for the mod, just put it on close focus and cover the inside of the helix with tape to keep the filing "shrapnel" out.

Its certainly not necessary to dissemble the helical, but I think its preferable, if only to be sure of preventing filings from getting into the focus helical or optical cell and possibly causing damage. Also, every Nikkor I've done this mod on has needed relubing anyway, so it was a no brainer for me to disassemble the helical and do both jobs at the same time.

Also note that the helix might be assembled differently, depending on the age of the lens (confirmed by Rotoloni):

Yep. I've done this mod to a couple of early lenses and they have two tiny screws that go in from the top instead of three screws on the side of the helical. The design is also quite different. The later lenses are definitely an improvement in terms of reducing play in the focus action. I'll be modifying an early Nikkor-H 50/2 in a few weeks and will snap some photos of that when I disassemble it.

 

[jonmanjiro]

Yep. I've done this mod to a couple of early lenses and they have two tiny screws that go in from the top instead of three screws on the side of the helical.

Here's a quick rundown on dissassembling an early version helical. The lens I'm dissembling here is a very early Nikkor-H 5cm F2 with no aperture click stops. The way to tell what type of barrel you've got is to look for a screw just above the infinity mark - no screw means early version.

Next, loosen and remove the optical cell retaining ring and remove the optical cell and shim from the focus helical.

Next, loosen and remove the two tiny screws and the retaining ring.

That will leave you with these three pieces and two tiny screws (don't lose the screws!).

Next, disassemble the helical.

Then make the cutout, clean and relube, and reassemble.

At reassembly, three parts have to be lined up perfectly to be able to reinsert the two tiny screws. Being careful not to damage the thread, I use a safety pin tip to line these three parts up.