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_nathan
Tinkerer
Username: _nathan
Post Number: 24
Registered: 04-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 28, 2009 - 07:22 pm: | 
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I have been attempting to disassemble a Canon 50mm f/1.2 LTM Rangefinder lens, however to no avail. I'd like to remove the front group of elements to access the rear group in order to remove a layer of haze. Unlike Leica comparables I cannot seem to remove the front grouping. Is this something to be left to a professional or is there a trick that I am missing?
Thanks all! |
Steve_roberts
Tinkerer
Username: Steve_roberts
Post Number: 26
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, January 30, 2009 - 04:01 am: |
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I've run into the same problem with dismantling a Pentax f1.2 50mm lens, ie can't work out how to remove the front element (I posted a question here a few months back but got nowhere). In the case of the Pentax, normally you'd just unscrew the ring with the lens info written on it for access to the front group, but when you try to do this that ring only unscrews as far as the filter thread, ie the filter thread is of a smaller diameter than the ring bearing the lettering inside it. I looked at the problem again a couple of nights ago and now wonder whether a small step in the lens barrel is because the filter thread ring is screwed in after the lettering ring. Perhaps your lens has a similar construction (if that's what it is)?
Perhaps there is some good reason why fast lenses such as f1.2 warrant a different front end construction with their much larger diameter front elements? Hmmmm!
Steve |
_nathan
Tinkerer
Username: _nathan
Post Number: 25
Registered: 04-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 03, 2009 - 11:13 am: |
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Steve,
Alas, it appears we are facing similar dilemmas! I was in fact able to remove the ring with the lens information on it with a spanner wrench, however I could not figure out how to proceed thereafter. There were no exposed screws, threads, etc. I'm stumped, like yourself, and tried entering from the back but the rear element will not budge. I would assume the sheer size of large elements makes for a different method of construction. I'd really love to remove the haze from this lens so I can add it to my outfit for low-light situations. I think I may send it out to DAG. Any further luck with your lens?
N. |
Glenn
Tinkerer
Username: Glenn
Post Number: 512
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 03, 2009 - 12:43 pm: |
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No, size makes no difference. I have no stripdown information on this pparticular lens, but are you sure that the name ring is just a 'decorator' and not the front element retainer? If it is the latter, the front element may just be a very tight fit in the recess. I have had instances of this type of construction where front element removal has required the use of a vacuum pump and large rubber sucker, the proprietary rubber bulb variety just did provide enough grip.
Close examination with a magnifier should indicate a visible lens edge, if the front ring is the actual retainer. |
Steve_roberts
Tinkerer
Username: Steve_roberts
Post Number: 27
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 05, 2009 - 07:12 am: |
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Nathan,
I tried unscrewing the possible front ring but couldn't get it to budge. Either I'm totally wrong and it's all one piece or it's screwed in tighter than I'm prepared to try to undo it without knackering the lens! One reason I can think of why my lens might be constructed that way is that it allows 52mm filters to be used, as per most other non-M Pentax lenses of the era (zooms etc excepted). I have to admit to being stumped. I like the lens so much for its virtually zero DOF that I may just have to go in search of another one!
Steve |
John_shriver
Tinkerer
Username: John_shriver
Post Number: 39
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 22, 2009 - 06:47 pm: |
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This lens goes together like all the Canon 50mm and wider rangefinder lenses. Remove the ring just inside the rangefinder cam (it has slots for a spanner wrench), and the entire optical cell can be removed from the focusing mount. There's a collimation shim in-between, don't lose it or mix it up with another lens.
The two lens blocks screw into the middle diaphragm assembly. Scribe them and the diaphragm assembly so that you know exactly how tight to screw them back in, and then unscrew them with a little torque. The rear group should be particularly easy to get out.
If you don't scribe them, the lens will probably be a different focal length when you're done, due to tightening them a different amount, and then the infinity collimation will be shot, which really matters on an f/1.2 lens.
Haze on that particular lens surface is a common, and sometimes recurring, problem with this lens. |
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