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Abe_in_space
Tinkerer
Username: Abe_in_space
Post Number: 1
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 25, 2011 - 01:19 am: | 
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I came upon a treasure trove tonight; my mother had some old M42 lenses lying around. One of them, a Carenar-branded 35mm f/2.8 has a problem: its focus ring doesn't seem to quite connect fully to the body of the lens in order to refocus.
Just to be clear, we aren't just talking about a small rubber part here; if it were that, I'd simply slip it off and rely on the metal, or find a way to reglue it. The whole focus ring itself has come unseated somehow.
When I press down just right as I turn, I can refocus somewhat, which leads me to think this is something I could possibly kludge together a repair for.
So far, all the disassembly I've done is to remove four screws on the bottom, removed the screw mount base plate (not sure of the technical term), and removed the aperture adjustment ring. I've also reassembled it and disassembled it once again, just to make sure I know what I'm doing so far.
Here are some pictures of the partially disassembled lens:
http://img43.imageshack.us/img43/2632/img0326zt.jpg
http://img402.imageshack.us/img402/963/img0329qwd.jpg
http://img535.imageshack.us/img535/5180/img0332od.jpg
Does anyone have any suggestions on further steps for disassembly/repair? Any help you guys could offer would be wonderful. |
Finnegan
Tinkerer
Username: Finnegan
Post Number: 88
Registered: 09-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 26, 2011 - 11:22 am: |
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I don't get why you are disassembling the lens from the back. Why don't you roll off the rubber grip and tighten the screws that are likely beneath it? |
Michael_linn
Tinkerer
Username: Michael_linn
Post Number: 37
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 26, 2011 - 12:38 pm: |
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If it's like other Petri-Carenar lenses I've seen, the front name ring and filter ring unscrews as one piece, revealing three or so screws below which attach the focus ring to the hekical. If that is the case, put the back part of the lens back together, put the lens on an M42 body with known good focus, focus the lens at infinity, and screw down the focus ring at the infinity setting. |
Abe_in_space
Tinkerer
Username: Abe_in_space
Post Number: 2
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 26, 2011 - 03:50 pm: |
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Finnegan, when I removed the rubber part around the focus ring, there were no screws, that'd why I assumed I had to go in from the back.
And Michael, thanks, but the focus ring and the name ring definitely seem to be separate. I tried what you suggested to no avail. The broken lens laughs at my efforts. |
Michael_linn
Tinkerer
Username: Michael_linn
Post Number: 38
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 26, 2011 - 05:21 pm: |
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Abe-
You are going to have to get the front lens barrel off to stop the laughing!
Try moving the focusing ring to screw the front lens barrel out as far as possible.
Look for setscrews. If you see just one, loosen it and unscrew the lens barrel. If you see three spaced evenly around the barrel, loosen them and pull off the lens barrel. You are going to have to get to those three screws underneath to solve the problem. If you get it screwed out all of the way, but don't find setscrews, try again to unscrew it by hand. It may take some effort.
If that does not work, perhaps you can unscrew the name ring by itself, which might give you the access you need. |
Finnegan
Tinkerer
Username: Finnegan
Post Number: 90
Registered: 09-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 26, 2011 - 06:03 pm: |
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Well, if you can focus it by putting pressure on the focus ring, and you can't fix it any way else, roll back the rubber and "dent" the metal so it always is applying pressure and it is "fixed". |
Abe_in_space
Tinkerer
Username: Abe_in_space
Post Number: 3
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 27, 2011 - 02:14 am: |
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Thanks so much, Michael. After a lot of experimentation with ways to apply pressure, I managed to get the front of the lens barrel out far enough that I could unscrew it by hand.
I've also managed to remove the three set screws, and succeed in reseating the focus ring. However, there remains one last problem: when I put it all back together, I have a much narrower ability to focus than I did before. I either have to sacrifice focusing on close objects, or sacrifice the ability to focus to infinity.
I can solve this problem by just doing away with the focus ring entirely and use the part underneath to focus, but obviously, as this was not designed for use without the leverage the focus ring applies, it's much more difficult to use.
I must be doing something wrong. Does it have something to do with the tightness of the set screws, perhaps? Something else?
Thanks again so much for all your help. |
Glenn
Tinkerer
Username: Glenn
Post Number: 958
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 27, 2011 - 10:23 am: |
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The major problem you have here is that one does not know why the focus ring was loose in the first place. If it had just worked loose the solution is to set the focus on infinity, by screwing up the helical with the inner part, then mount the focus ring on the lens with the infinity mark adjacent to the datum then insert and tighten the three screws. Unfortunately if somebody has separated the helical and then screwed it up at the wrong start position, you will never get the focus right without reassembling the helical properly - a long process by trial and error, but rewarding in the end.
I do not know what you are doing 'wrong', it appears all to be due to the actual extension of the helical and the positioning of the focus ring and focus limit stops.
Assume for starters that the helical is assembled correctly (you did not unscrew it?), remove focus ring and focus lens to infinity using very distant brick wall as target. Then position focus ring with infinity mark aligned with focus datum and insert screws. If you have not mucked about with with anything else all should be well.
If the helical needs proper assembly, choose a rainy weekend and a very comfortable chair. My preferred assistant in cases like that is a bottle of good Malt. |
Abe_in_space
Tinkerer
Username: Abe_in_space
Post Number: 4
Registered: 10-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 27, 2011 - 03:32 pm: |
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Glenn, thanks. And thanks to everyone else.
I think I must have accidentally partially unscrewed the helical in my attempt to unscrew the front of the lens barrel in order to get at the screws. I'll take a further look at it when I can. Fortunately, this is not an extraordinarily expensive or valuable lens, just a "found" one. In the mean time when I use it I'll just leave the focus ring off and use the "inner ring," so to speak. I was probably going to buy another 35mm anyway, maybe a Mir 24, or a 1B.
Thanks again everyone. |
Robbiechad
Tinkerer
Username: Robbiechad
Post Number: 1
Registered: 01-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, November 09, 2011 - 08:53 am: |
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This sounds like a Helios 44M-4 I got from ebay when I tried to focus it the front lens group and barrel fell out, the focus ring is secured by 4 screws but to get at them you have to remove the name plate ring then unscrew the front group and completely remove the helical, then as is said before getting them back together in the right alignment is the test, I have had two goes at mine and although it focuses Ok minimum distance infinity registers between 4 & 10metres, it is useable if you dont worry about the distance scale being right. I will have another go to try and get it correct it is a real pain though. |
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