lens repair, modification and disassembly guide thread
/forum/topic/1159122/1

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sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

Thatspeck wrote:
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


the minolta i'm using is the 55/1.7 not the 50/1.7. the length of the donnor lens doesn't matter for rangefinder coupling, what matters is the focal length of the optics (which in the case of the contax is actually 46mm). perhaps 46mm is close enough to 50mm to that using a cut copper pipe won't throw off of rangefinder focusing too much (i'm not sure). for truly accurate rangefinder coupling with non 50mm lenses i suspect you would need to attach the copper pipe to the part of the helicoid that rotates with respect to the lens mount and cut the pipe at a specific angle (calculated according to how much the helicoid moves the optics per unit of angular displacement) in order to get proper displacement of the rangefinder cam.



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

Looks like I've got more reading to do. Should be a great winter project and fits in well with my recently adopted "photography through suffering" (rangefinder) ethic Looks like thee 55/1.7 can be had even a little cheaper than the 50, quality helicoid for the price. I should have it done a day or two after Hawks offers the kit for sale



DamonJoyce
Registered: Aug 06, 2010
Total Posts: 239
Country: United States

sebboh wrote:
the minolta i'm using is the 55/1.7 not the 50/1.7. the length of the donnor lens doesn't matter for rangefinder coupling, what matters is the focal length of the optics (which in the case of the contax is actually 46mm). perhaps 46mm is close enough to 50mm to that using a cut copper pipe won't throw off of rangefinder focusing too much (i'm not sure). for truly accurate rangefinder coupling with non 50mm lenses i suspect you would need to attach the copper pipe to the part of the helicoid that rotates with respect to the lens mount and cut the pipe at a specific angle (calculated according to how much the helicoid moves the optics per unit of angular displacement) in order to get proper displacement of the rangefinder cam.


So what did you look for in choosing the 55/1.7? I wonder what other lenses could be used.



sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

DamonJoyce wrote:
sebboh wrote:
the minolta i'm using is the 55/1.7 not the 50/1.7. the length of the donnor lens doesn't matter for rangefinder coupling, what matters is the focal length of the optics (which in the case of the contax is actually 46mm). perhaps 46mm is close enough to 50mm to that using a cut copper pipe won't throw off of rangefinder focusing too much (i'm not sure). for truly accurate rangefinder coupling with non 50mm lenses i suspect you would need to attach the copper pipe to the part of the helicoid that rotates with respect to the lens mount and cut the pipe at a specific angle (calculated according to how much the helicoid moves the optics per unit of angular displacement) in order to get proper displacement of the rangefinder cam.


So what did you look for in choosing the 55/1.7? I wonder what other lenses could be used.


i was looking for the best focusing ring and helicoid of appropriate size and reasonable price. my experience shooting with and performing maintenance on a variety of different manual focus brands has led me to the conclusion that rokkor MC lenses are as good or better in this regard than any other slr lenses out there except for some leicas and the contarex series. i also really like the scalloped metal grips on rokkor focus rings. the 55/1.7 is comparably sized to the smaller contax g lenses, was a kit lens (meaning it should be cheap and plentiful), and has fast enough optics to necessitate a large interior for alternate optics and custom aperture linkages. also, i quite like the lens and had two of them on hand already.

on a side note: in the passage of mine you quote above i talk about using copper pipe. i misspoke, brass would definitely be preferible for such a task.



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

Without knowing the dimensions of the 45's optics block, or the internal dimensions of the nearly infinite variety of donors, it could become an expensive experiment. The 55 Rokkor looks like as good a bet as any and I've always loved that scalloped focus ring as well. That the 28 is focusing well beyond infinity though doesn't bode well for the 45, would probably need a good sized shim assuming the front end lands in the same spot, it's definitely longer.



sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

Thatspeck wrote:
Without knowing the dimensions of the 45's optics block, or the internal dimensions of the nearly infinite variety of donors, it could become an expensive experiment. The 55 Rokkor looks like as good a bet as any and I've always loved that scalloped focus ring as well. That the 28 is focusing well beyond infinity though doesn't bode well for the 45, would probably need a good sized shim assuming the front end lands in the same spot, it's definitely longer.


better to go to short than too long. there are few things easier to make than a 10mm spacer.



ZoneV
Registered: Nov 20, 2008
Total Posts: 882
Country: Germany

RCicala wrote:
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


sebboh wrote:
...awesome site! thanks.


Thank you both!

The big link directory is the main site there, with 10 years history of collecting photo DIY links. And still the list of links I should add is growing faster than I add links.

Roger, I have added links to your interessting defects statistics to my small growing typical defects list some weeks ago. But it seems I missed to load that update to my webspace yet.





ken.vs.ryu
Registered: Apr 24, 2005
Total Posts: 3437
Country: N/A

I need my g90 converted to M with the rf coupled.



Jacob D
Registered: Mar 30, 2009
Total Posts: 1757
Country: United States

Derek, what is the approx MFD of the lens now? Is it different than before?



sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

Jacob D wrote:
Derek, what is the approx MFD of the lens now? Is it different than before?


yup, the rokkor has approximately 2.5mm more focus throw so the mfd should be around 1ft or below i believe. using the helicoid adapter on it should bring it into the range of a real macro.



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

Sebboh, would you be willing to put up a pic of your "rubber ring" you used to remove the name plate on the 28G. My bottle cap and cut up rubber bands has so far failed to budge it. I got a cheap 55/1.7 and that actually has tiny spanner slots on the name plate. Surprising zeiss/Kyocera would tighten something using only friction. I'm hoping to retain the original aperture ring, it's just a hair smaller than the cosmetic black spacer on the Rokkor. (I'm working on the 45, dimensions may be different).

Looks like my LTM/M adapter is just big enough in diameter to span the mounting points. There is a silver cosmetic rim that comes off still attached to the Rokkor mount. Looks like that may be usable as gap filler assuming it doesn't require much of a shim. The length of the optics blocks are pretty close between the 45 and 57.



JimBuchanan
Registered: Jan 11, 2006
Total Posts: 1443
Country: United States

In the absence of or used with a rubber ring, try washing the talc off of a latex glove and wrap the disc or ring with the glove. It has pretty good gripping power.



sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

Thatspeck wrote:
Sebboh, would you be willing to put up a pic of your "rubber ring" you used to remove the name plate on the 28G. My bottle cap and cut up rubber bands has so far failed to budge it. I got a cheap 55/1.7 and that actually has tiny spanner slots on the name plate. Surprising zeiss/Kyocera would tighten something using only friction. I'm hoping to retain the original aperture ring, it's just a hair smaller than the cosmetic black spacer on the Rokkor. (I'm working on the 45, dimensions may be different).


the rubber ring i use is similar to these: http://www.ebay.com/itm/251167398684?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

i actually much prefer using these to a spanner wrench whenever possible because i don't like having hard metal that close to the lens and even when the spanner tips fit the notches perfectly they can still wear off the paint of retaining rings. they're also easier to provide even pressure to than a spanner wrench.

i believe the dimensions on the front barrel, aperture ring, and optical mount are identical between the g45 and g28. the main difference between them is that the nameplate of the g28 screws directly into the optical block while the nameplate on the g45 screws into the front barrel.

as to why zeiss chose not to leave notches for a spanner wrench in the nameplate, it's most likely for cosmetic reasons since the nameplate doesn't actually have any structural function. i do have a pet theory though that zeiss purposely tries to obscure the best methods for dissembling their lenses in an attempt to prevent uncertified people from performing maintenance on them.

Thatspeck wrote:
Looks like my LTM/M adapter is just big enough in diameter to span the mounting points. There is a silver cosmetic rim that comes off still attached to the Rokkor mount. Looks like that may be usable as gap filler assuming it doesn't require much of a shim. The length of the optics blocks are pretty close between the 45 and 57.


i was contemplating using that fake retaining ring on the rokkor as well, but thought it was a little thin. remember that how much of a shim you need depends on how close the rear element must be to the sensor at infinity not the size of the optical block.

let me know how it goes, i'm still waiting on my full sized ltm-m adapters (slow boat from china )



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

Had no idea there was a dedicated tool for that. I'll keep trying to make something though, the latex glove idea sounds promising. Thank you both

I think can finally add something that might be useful, at F2 and focused at infinity (not the infinity stop), the distance from the end of the black ring around the rear element of a Contax G 45 F2, to the face of the Nex mount (in this case a Metabones adapter), is .389" so then 1.098" to the sensor. An M mount register should be 1.100" so it looks like that black ring on the 45 should end up more or less flush with the face of an M mount at infinity (.001" makes a difference). Then as long as I was measuring things, my Hawks M/Nex adapter is .381" (Shogun is .289ish), the nex mount register is 18mm or .709" for a total of 1.090", explains why I can focus so far beyond infinity with those adapters. Hope this helps and I encourage any corrections to the above.

On the subject of LTM/M adapters, I've received two from Ebay seller "Jinfinance" that are full diameter, spot on thickness, and even have six bit pits machined in. Buy two, spring for EMS shipping and it's still less than one Voigt. and Less than a week to Oregon.
http://www.ebay.com/itm/200702156132?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I had worse luck with another seller, the threads were started in the wrong place so the RF cam cutout ends up at the bottom. Won't matter of course for this application and am happy to finally have a use for it.

This is going to be fun


Side benefit:
The optical block from the 55/1.7 Rokkor is going to make a fine loupe, just need to make a mount for it.



FlyPenFly
Registered: Feb 14, 2011
Total Posts: 6389
Country: United States

Great guide, can't wait to see how the 28mm F2.8 ends up.



Edgars Kalnins
Registered: Mar 09, 2007
Total Posts: 708
Country: Latvia

The hack looks very neat and more importantly - I might be able to do it . I will wait till the process is finished though, as I have never done such things before.



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

So far I'm still stumped at step 1 Looks like Micro-tools.com has those rubber rings though as well so shipping will be quick. I've tried a few things now without success and don't want to risk damage, the right tool is pretty cheap.

Looks like there will be a number of ways to do this Edgars, if my 45 goes well I may try the black 90G I got from you

I'm going to do some measuring on a Canon 50/1.4 rangefinder lens too as a donor, it has a 48mm filter diameter as well as a circular RF cam coupling.



Edgars Kalnins
Registered: Mar 09, 2007
Total Posts: 708
Country: Latvia

Thatspeck wrote:
So far I'm still stumped at step 1 Looks like Micro-tools.com has those rubber rings though as well so shipping will be quick. I've tried a few things now without success and don't want to risk damage, the right tool is pretty cheap.

Looks like there will be a number of ways to do this Edgars, if my 45 goes well I may try the black 90G I got from you

I'm going to do some measuring on a Canon 50/1.4 rangefinder lens too as a donor, it has a 48mm filter diameter as well as a circular RF cam coupling.



I will keep an eye on the progress. I had forgotten about the sale . In fact, I bought an inexpensive silver 90G just a couple days back, thought I should get one before the price goes too high. Good luck with the adaptation!



Thatspeck
Registered: Dec 13, 2003
Total Posts: 740
Country: United States

These will do the trick for removal of the vanity ring;
Click

$2.99 at the hardware store. Cut the ends at various spots to get different sizes. Now for the real work...

Edit: Done my best but pics won't display using basic html. Same way I've done it here many times before, somebody has changed the rules



sebboh
Registered: Nov 02, 2009
Total Posts: 10057
Country: United States

Thatspeck wrote:
These will do the trick for removal of the vanity ring;
<img src="http://im1.shutterfly.com/procgtaserv/47a2ce10b3127cce98548fcd47c800000035100AauWjRy5bM2VA">

I can't see why it's not displaying but I'm open to suggestions, or just cut and paste everything within the quotes. $2.99 at the hardware store. Cut the ends at various spots to get different sizes. Now for the real work...


nice!

it's not displaying because it's not a jpeg.

i'm still waiting on my m-mount adapters. should have gotten expedited shipping...



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