since there are number of people on the forum that like to do their own lens repairs and even convert lenses to other mounts, i thought it might be nice to start a repository for info on what people have done and how they've done it.

so anybody that has documented a lens conversion, repair, or simply a disassembly please post it here.

i'll start with how to remove the optical cell from the contax g 28mm f/2.8 biogon since a number of people expressed interest in how i am doing my ongoing conversion of the lens into the helicoid of a rokkor MC PF 55mm f/1.7.

it's actually a very simple disassembly. the most difficult step is the first step: removing the name plate from the front of the lens:



i use a rubber ring that i press against the name plate and unscrew it:



the next step is to remove the 4 screws under the nameplate (highlighted by green stars).

you can then simply lift the front of the lens barrel off:


at this point there is nothing holding the optical cell in the lens any more and it can be removed by simply turning the lens over and gently jiggling it. the entire optical assembly with aperture module will slide out along with a brass washer that sits between where the optical assembly is screwed into the helicoid:



and there you go, done. if you want to clean some dust out, the rear optical module easily unscrews from the aperture and front optical modules. the ridge on the optical assembly (that i've highlighted with the green star) opens and closes the aperture.

in my next post i'll explain how to disassemble the rokkor in order to put the contax optical assembly inside it.

disassembling the rokkor MC PF 55mm f/1.7 takes a few more steps, but starts the same way:



remove the nameplate:

next remove the 3 screws holding the front of the lens barrel in place (2 are highlighted by green stars):



next remove the 4 screws holding the optical assembly onto the helicoid:



you can then pull out the optical assembly:



note that there are 3 screws clamping the focus ring to the helicoid (2 are highlighted with green stars). these can be loosened in order to adjust where the infinity focus stop (and mfd) are on the helicoid just like they can on the rokkor 58/1.2.

now for the lens mount:



remove the 4 screws attaching the mount to the helicoid (3 are highlighted in green).



you are left with the helicoid and aperture ring. be careful not to lift the aperture ring off the body as well because you could easily lose the ball bearing. the 4 screw holes marked by the green stars above are where any alternative mount should be placed. a spacer/retaining ring should be placed below the new mount in order to hold the aperture ring in place.

the attachment to the aperture ring (highlighted with a green star in the photo below) travels in the same direction and roughly the same angular distance as the aperture control lever on the optical assembly of the contax g 28/2.8.



it can be seen looking through the other side of the focus ring helicoid as well:



note that the inner diameter of of the rokkor helicoid is greater than the outer diameter of the mounting ring on the contax optical assembly. this means that a washer with a larger radius will have to be put around the contax optical assembly in order to attach it to the helicoid.

i was able to do that with spare parts i had lying around as well as attaching a c-mount to NEX adapter to the base of the helicoid allowing me to mount the frankenzeiss lens on my NEX:



however it focused much past infinity. i'm currently working on making a more attractive front to the lens and putting a leica mount on it rather than an e-mount.

I can feel the prices of both these lenses doubling as I type this.

I have that same feeling.

I understand why you posted the details re: the disassembly, but I'm more interested in what you did for the aperture connection. Thanks very much for sharing.

And good idea for the thread, I'll add to it soon.

LightShow wrote:
I have that same feeling.

I understand why you posted the details re: the disassembly, but I'm more interested in what you did for the aperture connection. Thanks very much for sharing.

And good idea for the thread, I'll add to it soon.

yeah, i was waiting to get my spacers to make a less ghetto looking linkage. for my initial test i just used a christmas ornament hook – wrapped it twice around the piece on the rokkor's aperture ring and put the two ends around either side of the contax aperture tab. for the final version i'll probably bend a little aluminum sheet metal to the proper shape and screw it on to the rokkor aperture ring where the current tab is.

Sebboh,
I'm sure that I'm getting denser in my old age; but why are you doing this (other than that you can)?
John

John, it's because the Contax G lenses don't have a focus ring and rely on mount adapters with cruddy spur and pinion focus. This ingenious transplant gives the G lens a real helicoid. Not to mention whatever mount you prefer. Pretty cool!

Derek, have you investigated a similar transplant with either the G 45 or 90? Are you hacking a LTM to M adapter for the Leica mount? I can't imagine there being a cost effective way to rob an M mount off anything.

john_edwards wrote:
Sebboh,
I'm sure that I'm getting denser in my old age; but why are you doing this (other than that you can)?
John

so i can have a real, high quality focus ring on my contax g lenses instead of the jerky thin ring that turns the wrong way and works through the screw drive on the adapter. also, putting an m-mount on it means i can take them with me to just about any other mirrorless camera that comes out if somebody else comes out with a better (FF?) camera. oh and it focuses down to macro distances this way.

it should be noted – i'm not into this new fangled autofocus thing people seem to like now a days, so i'm not as interested in new lenses as i am in making sure the old lenses i love last as long as possible.

Jacob D wrote:
Derek, have you investigated a similar transplant with either the G 45 or 90? Are you hacking a LTM to M adapter for the Leica mount? I can't imagine there being a cost effective way to rob an M mount off anything.

yeah, i've got a few ltm to m-mount adapters on their way to me for the new mount.

i transfered a g45 to a rokkor 58/1.4 with an e-mount earlier, but i like this method better and the g45 will work the same (just needs a larger spacer). i believe the g35 will also work this way but i'm not positive. i'm interested in testing out the feasibility of doing something similar with the g21 and g90 as well, but don't have a driving urge to buy either of those lenses now.

Good work, sebboh.

I'm semi interested in doing a G28 remount, but with the $400+ going rate for a G28 lens, plus $100 for donor lenses and parts, I'm not sure of the cost/benefit considering I have the ZM25, and the G28 is at least if not more symmetrical with the need of a corner fix. I do say that the G28 has a better MTF than the ZM28, though.

I have been waiting for over 6 months for a Hawk G45/M mount conversion that I was going to deconstruct for possible conversion ideas, but I could have easily bought a ZM50 for equal or less money.

The ltm-M adapters may not have the diameter you need for screwing to the Minolta lens body.

Don't you have a Minolta 28/2.0? and how does it compare to the G28 on the N7?

JimBuchanan wrote:
Good work, sebboh.

I'm semi interested in doing a G28 remount, but with the $400+ going rate for a G28 lens, plus $100 for donor lenses and parts, I'm not sure of the cost/benefit considering I have the ZM25, and the G28 is at least if not more symmetrical with the need of a corner fix. I do say that the G28 has a better MTF than the ZM28, though.

I have been waiting for over 6 months for a Hawk G45/M mount conversion that I was going to deconstruct for possible conversion ideas, but I could have easily bought a ZM50 for equal or less money.

The ltm-M adapters may not have the diameter you need for screwing to the Minolta lens body.

Don't you have a Minolta 28/2.0? and how does it compare to the G28 on the N7?


the cost issue has changed a bit since i bought my g45 for $200, but i think even at current contax g prices the g28 and g45 conversions will still be around $300 cheaper than the cost of the zm version. i do like the g mtfs better for both lenses as well, though the zm lenses probably have better coatings and have more aperture blades. the rokkor 55/1.7 is basically a $25 dollar lens (though a very nice one).

the ltm-m adapters that have an uninterrupted outer diameter (instead of the ones where the outer diameter is shorter for part of the circumference) could be screwed into the tapped holes on the minolta lens body. i'm not planning on actually doing that though. my plan was to attach the spacer to the lens body and put tapped holes in the spacer with which to attach the adapter.

the g28 and rokkor 28/2 are very different lenses look wise and the rokkor is nearly three times as long with the adapter making the camera/lens combo lose it's compactness. the contax is definitely higher contrast with lower CA and probably also sharper (but i haven't done any comparisons). the g28 does have a little smearing on the NEX-7 in the corners (but looks pretty good on the 16mp sensors).

Thanks a lot for the pics and descriptions, sebboh!

freaklikeme wrote:
I can feel the prices of both these lenses doubling as I type this.

Not really. It's not like anyone can do this conversion at the kitchen table, and I even doubt that the conversion would raise the value of the lens. There's just not enough enthusiasts who would accept the butchered looks to get the performance.

Thanks, makes perfect sense!

sebboh wrote:
..so anybody that has documented a lens conversion, repair, or simply a disassembly please post it here.
...

I do not rewrite things I have written already on my homepage, or even worst copy and paste.
Starting with the older ones, back 2009:

Homemade tilt lens out of old Canon FD 50 and 28 mm lenses - only for crop DSLR.

Fungus cleaning on a Vivitar 24mm f/2.8 (German text)

Minolta Rokkor 58mm f/1.2 mount conversion to EF mount

Fungus Cleaning on an Rodenstock Apo Rodagon 50mm f/2.8 enlarger lens - German text

Minolta Rokkor 35mm f/1.8 EF mount conversion, quick and dirty - German test

Canon FD 300mm f/2.8 L EF mount conversion

Canon FD 100mm f/4 Macro conversion to EF mount - German text only

Canon Fd 500mm f/4.5 conversion to EF mount

Canon FD 400mm f/2.8 mount conversion - German text.
Until then Ed Mikas adapters where not avialable and tested for these lenses

Canon FD 85mmf /1.2L reversible mount conversion, no infinity here. Most of my mount conversions are reversible. German text only.

Samyang/Falcon/Boyer/Walimex 14mm f/2.8 focus scale adjustment - register distance way.

Novoflex Noflexar 60mm/4 bellows-head fungus cleaning. German text

Bokeh optimizing with apodization filter. Show on Helios 44 58mm f/2

Canon FD 24mm f/1.4 L mount conversion to EF EOS mount

Som Berthiot 75mm/1.8 projection lens focus helicoid for use on EOS

Nikon EL Nikkor 50mm/2.8 enlarger lens fungus cleaning

Carl Zeiss 35mm f/2.8 focus helicoid for focus stacking

Contax Carl Zeiss 18mm f/4.0 optimizing for Canon EOS 5D

Automated EOS EF iris in manual lenses integration

Minolta Rokkor 28/2.0 and 100/4 and others with Minolta lens to Canon EOS adapter, lens modification needed, but lens still can be used on Minolta cameras - without iris auto functions.

Sigma YS 135mm f/2.8 as Nikon DC defocus control "copy", spherical abberation could be controlled. Images from Trioplan to soft focus could be made with one lens. But much more effort to make images, extension rings needed. Not as fast as Nikkor 105 and 135 f/2.0 lenses..

Some of my DIY work is not documented yet. Probably I could write more this winter...

Markus, I was about to link to your DIY page: http://www.4photos.de/camera-diy/index-en.html

I didn't realize you were a member here, so it's a nice chance to say thank you for that page. It is most useful!!

Roger

ZoneV wrote:
sebboh wrote:
..so anybody that has documented a lens conversion, repair, or simply a disassembly please post it here.
...

I do not rewrite things I have written already on my homepage, or even worst copy and paste.
Starting with the older ones, back 2009:




awesome site! thanks.

I may have access to a high quality 3D printer. I wonder if it would be possible to make a spacer and step-up washer (for the optical assembly) in single piece. It would be ABS plastic, but that shouldn't matter since all the screws are mating trough the C-mount to the original helicoid.

sebboh wrote:
since there are number of people on the forum that like to do their own lens repairs and even convert lenses to other mounts, i thought it might be nice to start a repository for info on what people have done and how they've done it.
thanks a bunch! just ordered a 55/1.7

Nicely done Sebboh, I too am tired of waiting and would really like to have my 45/F2 in M mount and RF coupled. Assuming the Minolta 50/1.7 is in fact a 51.6mm focal length, would it matter that the optical block is 45mm? With the minolta helicoid and a piece of brass pipe like this;
http://www.rangefinderforum.com/forums/showthread.php?t=113676
Might work

DamonJoyce wrote:
I may have access to a high quality 3D printer. I wonder if it would be possible to make a spacer and step-up washer (for the optical assembly) in single piece. It would be ABS plastic, but that shouldn't matter since all the screws are mating trough the C-mount to the original helicoid.

yup that should work. it needs to be fairly rigid plastic to ensure that that the optical assembly is held in alignment with the focal plane though. i was contemplating going that route myself to save time in the shop, but wanted to include an external lens barrel on that piece rather than using the rokkor's for improved cosmetics.