NikonGear'23
Gear Talk => What the Nerds Do => Topic started by: simsurace on January 07, 2020, 18:03:14
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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.
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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?
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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 (https://www.fredmiranda.com/forum/topic/1546861/0#14496721).
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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,,,,
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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.
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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,,,
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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.
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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.
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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.
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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.
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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.
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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:
(http://www.suracephoto.com/wp-content/uploads/2020/01/IMG_9868.jpeg)
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.
(http://www.suracephoto.com/wp-content/uploads/2020/01/IMG_9869.jpeg)
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.
(http://www.suracephoto.com/wp-content/uploads/2020/01/IMG_9873.jpeg)
Inner (front, non-rotating) part of the helicoid.
(http://www.suracephoto.com/wp-content/uploads/2020/01/IMG_9871.jpeg)
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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 :D
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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...
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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.
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Interesting project, looking forward to see images from the resulting setup.
It certainly gives thought for other projects :)
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Looks good so far, always better to have a little too much clearnce rather than too little ;D Great progress!
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Interesting project, looking forward to see images from the resulting setup.
It certainly gives thought for other projects :)
Happy you find it interesting. I am curious to see the finished lens too.
However, I have to find another donor lens. I don't know what happened, but after I press-fit the Contax Zeiss outer helicoid into the Topcor inner helicoid, I could not get the Topcor helicoid back into the Topcor outer helicoid. Maybe the press-fit led to an expansion or I otherwise messed up the thread. I will have to try with another one (luckily they are abundant and cheap) and proceed more cautiously next time.
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Watching the process with much interest, Simone!
Hope you can sort out the causes of the problem.
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I now have a working prototype. The lens focuses to infinity (easy to calibrate this using the old and the donor helicoid together) and down to about half a meter as designed, but aperture control is not very nice. I‘m using a stack of step up/down rings to hold the aperture ring until I figure out a better way. First test shots and a more detailed explanation of the mod will follow.
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Congratulations on getting it to work! Very well done ;)
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More details about the mod:
1) I bought a cheap Topcor 53/2 lens. 50/2 should work as well, but I managed to screw up (pun intended) the helicoid of the lens I first bought (see posts above), so I had to shop for another one which turned out to be 53mm. The focus ring looks a bit cheaper in the 53mm though, so I would recommend a 50mm if you can find one.
Remove the optical assembly and all the aperture and bayonet locking mechanisms (springs, screws and levers). Remove both helicoids and mark their separation points.
Clean and set aside the helicoids for later.
2) I bought a cheap Fotasy M39-Nikon Z adapter. I removed the 2.5mm set screws that hold the M39 threaded insert and took out the insert. I then drilled and tapped the holes for M3 in order to use longer M3 set screws with pointed conical tip. After removing a hair of the inner diameter of the adapter with a rounded file, the Topcor rear shroud fits inside the Fotasy adapter. Position the two parts correctly, check for planarity with a micrometer, and then use a 2,5mm drillbit to make small conical holes in the Topcor rear shroud, aligned with the M3 holes in the Fotasy adapter. The M3 set screws will bite into those, holding the two parts together.
3) Remove the Topcor rear shroud. Use a Dremel cutoff wheel or similar to cut off the rearmost section of the shroud flush. It should look like this:
(http://www.suracephoto.com/wp-content/uploads/2020/01/E29C1873-C8E0-478D-82C5-542A1C906CCB_1_105_c.jpeg)
After putting it back into the Nikon Z mount, it will look like this:
(http://www.suracephoto.com/wp-content/uploads/2020/01/AB85B26B-3527-4EE6-9962-7CD27668161B_1_105_c.jpeg)
Like this the rear shroud will not vignette. However, the shinyness of the cut surface is not ideal. At a later stage I will paint it black. Any suggestions on which paint to use?
4) Cut off the rear part of the Contax Zeiss 45/2 outer helicoid. Use a small file to remove a bit of material around the outer diameter. Here I did one pass:
(http://www.suracephoto.com/wp-content/uploads/2020/01/76AE28D4-BED0-4E37-B9D3-68A4E7DA38C4_1_105_c.jpeg)
Remove just as much as you need in order to be able to press it into the Topcor inner helicoid without excessive force (I used my hand and a few light taps with a mallet. Do not use more force as I suspect it might deform the helicoid (anyway, this is my only explanation for how I screwed up the previous one, where I used a vise to press in the part without having first removed a bit of material).
5) After re-greasing the topcor helicoids and reassembling them, the Zeiss inner helicoid can be screwed into the Topcor inner helicoid (with its new insert). Place the optical assembly:
(http://www.suracephoto.com/wp-content/uploads/2020/01/C0FD49B4-A581-4DA6-912D-9202629E52A8_1_105_c.jpeg)
Be sure to use a micrometer or caliper to check the planarity of the setup at each stage of assembly (both of two parts that are mounted together, as well as cumulatively, i.e. relative to the Nikon Z bayonet mount).
6) The whole rig can now be mounted onto the camera for infinity calibration.
Leave some leeway in the Topcor outer helicoid for later calibration by using the position of the focus ring before drilling some holes or using epoxy to permanently secure the Zeiss inner helicoid to the Topcor inner helicoid.
The front part of the lens is currently not finished. The 53mm lens focus ring has a 55mm thread, into which I can screw 55-58, 58-55, 55-52, and 52-55mm step-up/down rings. The Zeiss aperture ring sits in this stack and is being gripped by the rings. I can thus control the aperture. The main reason for putting this temporary solution is to prevent dirt from getting into the helicoid, which is otherwise exposed. The Zeiss front section (into which the front bezel is screwed) fits snugly in the 52mm ring, almost sealing off the whole lens. However, the aperture ring now rotates along with the focus ring, which is of course not very efficient in use. Finding a permanent and workable solution for the front will be the most challenging part, getting the lens to focus correctly was actually easier than expected!
To be continued...
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Congratulations on getting it to work! Very well done ;)
Thanks! It was a good learning experience.
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and
did you take photos with the setup?
was it worth the effort?
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So far I only have a few test shots. The lens has a good reputation but I think such a conversion is only worth it if you have the lens sitting around unused as I did, and cannot sell it because it is broken. There are plenty of normal lenses. This one stands out because of its small size. I would guess that the Loxia 50/2 Planar could be a good alternative.
The lens produces nice and contrasty images. Around f/8 (don't have an aperture scale yet so I don't know precisely).
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2087.jpg)
Focused at infinity at f/2.
The lower part of the image is less sharp than the upper one. I will have to slightly tilt the optical assembly in order to correct this.
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2072.jpg)
center crop:
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2072_centercrop.jpg)
corner crop:
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2072_cornercrop.jpg)
Close to MFD at f/2. Bokeh is pleasant for my taste and quite unusual in its combination of smoothness and distinct edges. It reminds me of my Distagon 35/2 ZF.
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2082.jpg)
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2085.jpg)
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2079.jpg)
Closed down, the lens produces beautiful 6-pointed stars. This shot is at f/16 (minimum aperture). I will post another one with a proper sun as soon as I get an opportunity.
Sensor reflections are visible. I expect this aspect to improve somewhat after I will have painted or flocked the rear shiny parts of the lens.
(http://www.suracephoto.com/wp-content/uploads/2020/01/Z6_2066.jpg)
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Two more samples wide open. I do not find any faults with this lens, nice rendering and sharp across the frame.
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After a bit of milling, drilling, and filing, I now have a working inner barrel with aperture ring, made from the original Contax lens parts. The clicks are still missing.
I went back to the silver focusing ring from the Topcor 50/2, but since I‘m using the helicoid from the 53/2, I had to drill new holes for the set screws holding the focusing ring and helicoid together. I have to get shorter screws for that, though.
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The rear of the lens after spray painting.
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Simone, this is an amazing job! The lens looks like a real "product"!
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Sure does ;) and nice images as well, really compact lens that delivers big time, Bokeh is nice and creamy.
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Simone, this is an amazing job! The lens looks like a real "product"!
Thanks Akira, it starts to have a charm common to restored products that are cobbled together from non-original materials. It is amazing how much can be done by combining existing parts -- so far I did not have to add any new material apart from the bayonet mount and the set screws, everything else is done from original parts of the two lenses. For example, the part from the Contax lens that I'm holding loosely in reply #11, was cut right where the thin section ends, and the thin section has an outer ring that can be removed. The exposed part (approx. 10mm long) fits into the Topcor 50/2 focusing ring, not too tightly but maybe with half a mm of space. So I when I cut the part, I left some of the large diameter section and then removed just enough to give a sliding fit (maybe 0.1mm of space to prevent it from rubbing). Of course this does not provide weather sealing but is good enough for now. I guess with better tools one could even put a groove for an O-ring there. The original stack holding the aperture ring can now be attached with the original screw. By using some tape, I achieved a tight fit between the ring that attaches to the front of the lens assembly. This will be attached properly with screws later. What remains to be done:
- shim the lens correctly to fix the slight tilt of the lens assembly resulting in unequal sharpness in the upper and lower half of the image.
- affixing part of the original helicoid case that has the indents for the ball bearing for the aperture clicks. This will be tricky to get the tolerances right and assembly will be tricky as well, but we'll see how it goes. Worst case the lens stays de-clicked (as there is no CPU contact it does not matter anyway whether one sets a precise f/stop or not).
- screwing the front barrel together.
- some cosmetics. E.g. I don't like the gap between the DOF scale and the mount. I want to use some leftovers from the Contax lens to wedge in-between.
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And here, just for fun, a comparison to the 50/1.8S
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I'm getting closer to a proper clicked aperture. I cut off part of the original helicoid case that has the indents for the ball bearing. The two little feet are limiting the travel of the aperture ring in the stop-down direction, preventing the lens to be stopped down beyond f/16 (the markings on the outside of the aperture rings are for f/2...f/16). I lost the little steel ball at an earlier stage of the project, and did not note the diameter. It is probably 1.5mm in diameter. Now I have to source such a ball. I do not know yet how I can put the ball and then mount the lens without touching it. Maybe the grease will be sufficient to hold it in place, but the assembly will be quite tricky. We'll see...
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Most bearing suppliers can supply a large number of 1.5mm or 1/16" ball bearings for very little money - buy many of these, as loosing these small sized ball bearings is almost a given. Check out the industrial areas in your city for suppliers.
A small dab of grease has certainly helped me when reassembling lenses.
Great work by the way - a most informative thread.