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I have been asked to write up how I squeezed the glass of a Contax G Planar 45mm into the body of a Zuiko 50mm Macro, and attached it to a Sony NEX.
Planar 45mm Contax G within a Zuiko housing, for Contax G by meizzner, on Flickr
Planar 45mm Contax G within a Zuiko housing, for Contax G by meizzner, on Flickr
I did not take photos during the modification, and despite the acceptable (to me) result, I did some things wrong. Here I am writing how to do it better.
Probably here at the beginning is the right place to say that this is not easy.
Better try it only if you have already made some surgery on other lenses before.
Sometimes it may be hard to understand what I mean. English is not my native languange.
But if you have the parts in front of you, you will know what I mean.
If someone could point me to an explosion drawing of the Planar45 and the Zuiko50, I could perhaps make it more clear.
To start with: opening the Zuiko was difficult for me. I could not find the solution.
I finally cut through the recessed metal part in front of the lens because this part is not needed. It was a mess... poor Zuiko.
Now, reference is made to the pictures:
A) This is the (silver) Contax front part. This and the tube that contains the glass elements is all tht is needed from the Contax lens.
There is the thread for the filter, then a flange right behind the label-ring which says "Planar T* etc.", and then some 1 mm rear tube.
This rear overhead, about 1 mm, has to be removed until the flange itself is the most rear part.
Just grind it or use a lathe.
B) This is the front ring from the Zuiko. The white aperture marker at the top still belongs to it - it is one part, up to there.
The inner diameter of B needs to be extended, about 0.5mm, so that A fits inside. You could also reduce the outer diameter of ring A, instead.
Then, A+B are glued together. A+B need to be precisely in one axis, since this holds the entire lens together as we see later, and it also needs to guide the movement of the aperture ring D.
C) Part C is not visible in its entirety. It is the lens itself. It is one metal tube with glass and aperture inside, taken from the Contax. The front flange diameter must be reduced so that C fits into E. Part C is glued together with part A (I did not use the original Contax screws because the Zuiko part E was too narrow to have holes drilled, and threads cut).
The aperture lever which sticks out from the Contax tube is cut half way, so that the whole part C can be inserted from the front into part E.
D) The aperture ring needs little modification. Remove everything and attach something very thin and stiff to it, which has the correct shape to guide the (half-cut) aperture lever of part C. I did not try to have the klick-stop bearing included again, since the f-stops of the Zuiko and the Contax are different, anyway. That means, aperture will move fluidly, not in steps.
Luckily, the Zuiko allows more movement of the aperture ring than the Contax, which means the Contax can be fully opened and closed and only the movability of the Zuiko ring is not fully used.
E) The inner helicoid is invisible on the pictures. It sits behind/within part D. The inner helicoid has a long slit in circumferential direction, somewhere close to the front, where the Zuiko aperture coupling could enter from the side. I opened the long hole with two little cuts from the front, so that a gap is there where the aperture lever can enter from the front. Otherwise it will be impossible to assemble the lens with the new aperture coupling.
F) Behind the rubber are 5 screws. Not much to be done here, just open it in the beginning, and when finished, fine-tune infinity here.
G) This is the housing. I did shorten it from the rear end. However, if I did it again, I would leave it as it is.
H) The Zuiko mount is completely removed at the rear surface of this part H. There will be no Zuiko mount left, just the plain flange surface.
J) This is the rear end of a M42-NEX adapter. If you leave part G as it is (recommended), this part J needs to be about 2mm shorter than on this picture! Just try, or calculate the distances yourself. This new NEX mount has drilled and sunk holes for the screws. The holes correspond with part H, so that the screws go directly through part H, and attach in part G. Part H can be glued to part J.
One important issue in this process is that the tube with the glass elements could not be fixed to the front of the inner Zuiko helix, like it normally should. See section "C" of this description.
There was just not enough thickness available at the inner helix, to drill holes and cut threads.
I solved it this way: the rear part of the inner helix is narrowed. This tube-shaped part has kind of a "bottom".
The Contax metal tube with the glass elements inside has to protrude through a hole in this bottom (hole to be widened).
I attached the two parts to each other there, so that the tube holds the entire lens together from back to front.
I did it with epoxy, but it would be nicer to have that done with screws, somehow.
Therefore if one needs to clean the inner element surfaces of the lens, it can be opened from the front but not from the back.
If the last step is done with a screw connection instead of epoxy, it could be opened from the back, too.
After everything has been cleaned up, lubed and put together, the feeling of the lens is great! Everything turns smooth.
The distance scale is not accurate but usable.
All Contax F-stops are working. The Zuiko and the Contax apertures, by the way, turn in different directions. That means the lens would now be wide open where the scale originally read "22".
Therefore, and because the values would never correspond, the Zuiko F-stops are painted black. I want to attach a new scale to it but don't know yet how this shall look like.
The optical quality is not compromised. The Contax is one block of elements (without floating elements) and there's nothing that could get in unorder.
Hope somebody understands all of that halfway, what I have written.
Please tell me if one of you attempt to do the same!
I am thinking about a donor lens for the Contax G 90 F2.8 :-)
Here's one more picture from the rear angle:
Contax G Planar within a Zuiko body, ready to be used on a NEX by meizzner, on Flickr
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good work!
