Zeiss Planar 45/2 transplant

[simsurace]

I have a Zeiss Planar 45/2 lens for Contax G sitting around gathering dust. It is has broken focusing gears (and other problems) and therefore adapting it using one of the off-the-shelf adapters is out of the question. The optics should be fine, however, and thus I am contemplating removing the optics and putting them into some helicoid in order to use them as a very compact normal lens on the Z6. Has anyone here worked on this lens and is able to recommend a suitable helicoid? What about possible ways of setting the diaphragm?

The Contax G flange distance is 28.95mm ± 0.02mm and the Nikon Z is 16mm, but if I remember correctly the optics are not in the extreme position when focused at infinity on a Contax G body (i.e. the lens can focus past infinity), so the position of the optical elements will have to be calibrated anyway.

Maybe even parts of the existing lens can be reused instead? Happy to hear your thoughts...

If and when I do embark on this operation I will of course document the process.

Attached images show the lens and the broken gear.

[Hugh_3170]

Can you find a Contax G to Nikon Z adapter and simply remove the lens's gears which in a mirrorless camera such as the Z6 are not needed?  Or is there more to it than this?

[simsurace]

Those lenses do not have a focusing collar. The focus is set through the gear system even when using one of the off-the-shelf adapters. So removing the gears would leave the lens without a way to set focus. That's why I think I need to transplant the optics into another helicoid. It would be nice to be able to reuse some of the original lens barrel. I found a similar conversion (to what I'm imagining) being done for the Sonnar 90 over here on FM https://www.fredmiranda.com/forum/topic/1546861/0#14496721.

[Erik Lund]

Well, that is is a 90mm lens, where there is space behind the optics for fitting and adjustment. With a 45mm you get very little space to do anything also the thread pitch should be finer.
IMHO keeping aperture functionality and infinity focus,,, it's a job for a very skilled DIY and a big portion of luck finding another rear lens with a suitable focus pitch or it will be very difficult to find focus,,,,

[Akira]

Apparently, the modification is doable.  A Japanese expert shop of camera restoration/modification undertakes this very job you need but with quite high price (sorry the text is all in Japanese):

https://www.hayatacamera.co.jp/services/miyazaki/

Six lenses from above are all modified Contax G lenses.  You can click the thumbnails to enlarge.

[Erik Lund]

Thanks Akira! Basically same price as the lens itself,,, So I see why one would like to DIY
Looks like they are custom made to fit, not cheap but possibly the only way to do it reliable.
BTW they look very nice!
Miyazaki Optical do nice work I have had/used a couple of the Leica M lenses
Rangefinder coupling makes it of course more expensive,,,

[simsurace]

Thanks Akira and Erik!
I am somewhat optimistic it can be done. There is about 13mm of surplus space because of the difference between the flange distances of Contax G and Nikon Z.
The extension of the inner barrel on the original 45/2 lens is about 7mm from slightly beyond infinity to close focus. I would not mind if I find a helicoid that travels a bit further, but most that I have seen on ebay (e.g. Nikon Z to M42 helicoid adapters) have something like 30-40mm of travel which is way too much. So one idea I have is to find an old for-parts Pentax K-mount 50mm-ish lens with working helicoid and gut it. If I am lucky, I can fit the inner part of the original helicoid into the donor inner lens barrel. The extension should be similar to that of the 45mm lens. Pentax lenses have the same rotation direction of the focusing ring as Nikkors, which would be preferable. But if you have any ideas where to source a suitable helicoid I would be happy to hear them.

[Erik Lund]

Make sure to pay attention not only to length as such but also the pitch of the helicoid, usual universal helicoids are too steep IMHO for this application.

[Akira]

Although I cannot guaranty that it will work, I would look for an old Russian M39 lens like this Helios 44 58mm/f2.0 lens as a barrel donor:

https://www.ebay.com/itm/The-lens-Helios-44-2-58-m-39-for-Zenith/274183731240?hash=item3fd69fb828:g:5tMAAOSw7gleELtv

As you would know, Zenith M39 mount is the same thread as the Leica thread mount (LTM), (Strictly speaking, there is slight difference of the thread pitch: 1mm vs. 26/25.4mm, but practically interchangeable) but the same flange back as M42 mount (45.46mm).

So, if you use a LTM to Nikon Z adapter, the Zenith mount lens barrel can be mounted much closer to the camera, and thus you can have more room for the infinity adjustment.

[Akira]

In fact, BORG makes various camera mount and M42 thread adapter ring, and you would be able to do the same thing as I mentioned in my post above:

https://nikongear.net/revival/index.php?topic=9130.0

But, unfortunately, Nikon Z, Canon RF and Leica-Panasonic-Sigma L-mouints are so new that BORG hasn't yet made the mount for them.  Although it is very likely that they would make ones sooner or later, it won't be any immediate solution, unfortunately.

Nevertheless, I mention this here as a possible way for the conversion for the future reference.

[simsurace]

Thanks for the suggestions. I was thinking of a slightly wider barrel than what the Zenith seems to be, but I will look at old M39 or M42 lenses as well. I disassembled the lens yesterday, but haven't taken any measurements of the plastic part that holds the optical assembly. I will do so later and post some pictures.

[simsurace]

After fully disassembling the lens, I think that the lens can be modified and reassembled in a way that makes it a manual focus lens. The advantage over transplanting it into a foreign lens barrel would be that the pitch/travel of the helicoid is already right and the lens would largely keep its appearance. The amount of rotation is approx. 135 degrees, which is not too short for a normal lens.

My plan is the following: the part of the outer barrel that is normally fixed to the inner bayonet (which rotates to lock the mount) can, I think, be connected to the rear part of the helicoid (the part that rotates and is normally connected to the screwdriver via three gears) through a window in the helicoid case with a long screw. In order to make this possible, some protrusions of the helicoid case will have to be ground away in order to allow that part of the lens barrel to rotate more freely. Meanwhile, the inner part of the bayonet will be screwed to the helicoid case, which will necessitate some additional holes. Thus I believe that the remaining part of the lens barrel can be assembled as in the original lens, preserving the aperture control mechanism.
The second stage of the conversion will consist in attaching in some way a Nikon Z bayonet. One of the Contax G to Nikon Z adapters should then work, even though its focusing mechanism will not serve any purpose.

Any thoughts?

All the parts laid out:


Any ideas what the large spring is for? It was pressing against the inner (front) part of the helicoid away from the camera. But I'm not clear what purpose it would serve in a manual lens.

Optical assembly with aperture lever.


Helicoid case with window through which I plan to connect the rear helicoid to part of the lens barrel (silver part, also shown) for a makeshift focusing ring.


Inner (front, non-rotating) part of the helicoid.

[Erik Lund]

I have difficulty following what you intent to change,,,     
Maybe a drawing could help you also?with lens helical, mounts and other parts and then the camera flange as well
Spring is an Enigma   

[simsurace]

Yeah I realize that the explanation was not easy to understand. Anyway, upon further thought it does not seem as easy as I thought yesterday... there are too many protrusions in the plastic helicoid case and it will not be easy to reassemble with the modifications. So I'm still contemplating a transplant. I need to find a cheap donor lens nearby...

[simsurace]

The new lens is slowly taking form. I obtained an old Topcor 50/2 lens which serves as a donor. First I used electrical tape to see where I roughly end up with the optical group (fitted in the original inner helicoid. The mount is a Z-M39 adapter without the thread insert. The rear shroud of the Topcor will have to be modified.
The Zeiss outer helicoid fits into the Topcor inner one. So the Zeiss helicoid can be used for calibration.
The next step will be to figure out a way to close the gap with the old Contax lens barrel.