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11-09-2012, 03:53 PM   #16
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Thanks for all the replies.
QuoteOriginally posted by MysteryOnion Quote
I've fix two of my lenses with just a dot of contact cement on either end of the strip. The little amount was in case I had to adjust it later because I missed. No issues so far.
That's a very good idea, I will try to do as such too.

QuoteOriginally posted by geoffox23 Quote
Thanks cyclone3d

Your research is appreciated, and I have purchased a tube to try.
I'm presently using white lithium grease, but want a little less resistance.

Cheers
Geoff
Could you please keep us posted? I'm curious to hear your opinion about it before I buy anything.

11-17-2012, 11:20 AM   #17
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I have purchased a PTFE based lubricant spray, hope it will be fine.
However, upon disassembly of the lens and cleaning of the helicoid, there was still a stiff spot. I'd like to rule out the possibility of the helicoid being bent, so my only option is to completely remove it and clean it. I know that it is multi-entrance, so I'd like to avoid the PITA of having to guess the correct entrance when reinserting it.
Any tips, please?
11-17-2012, 03:47 PM   #18
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Too late for warnings and don'ts, as I've already dismantled it and found the culprit in this piece in the foreground. I have a feeling that I'm going to have a hard time with this.
Basically what it does is that the threading of the brass piece is not smooth, it goes a little stiff in a place, and then shows more and more resistance each turn. I have tried cleaning the threads thoroughly, but seems to have solved nothing. The pieces don't look bent either, and I don't think they've been fiddled with before.
In another order of ideas, can somebody please explain me how is this focusing system supposed to work?
11-17-2012, 05:19 PM   #19
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QuoteOriginally posted by kcobain1992 Quote
... then shows more and more resistance each turn...
Are you sure the lens has not been previously fiddled with? It sounds like the brass piece and the helicoid have different thread pitch.


Steve

11-18-2012, 02:36 AM   #20
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Yes, I'm sure they have the same pitch. As I said, it's stiff just in one point, other than that it's smooth.
11-18-2012, 03:12 AM   #21
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Have you relubricated the threads yet? Maybe that's all that is needed to get rid of the stiffness.
11-18-2012, 03:23 AM   #22
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Yes, it's not a lubrication problem.
11-18-2012, 10:15 AM   #23
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Might the lubricant be of a type where the sheer resistance increases under pressure?


Steve

11-18-2012, 10:33 AM   #24
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I don't think so, I also tried removing the grease and the stiff spot was still there. I don't know what could be wrong, the threads look clean, but there's something causing friction in one point. I can't even tell if it's not actually supposed to be like that. I imagine that if it were bent, it would be stiff more than in just one place... (and noticeable to the naked eye)
Can somebody point me to a tutorial about how are these 3 pieces supposed to work together? Maybe if I understand the principle right, I will be able to get by with not screwing the brass piece completely in, so the friction is lower.
11-18-2012, 10:57 AM   #25
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https://www.pentaxforums.com/forums/maintenance-repair-articles/179884-pentax...-database.html

This may be of use:
http://forum.manualfocus.org/viewtopic.php?id=13679

Perhaps the rings are misaligned? See Post #14 in the above thread.

Though not the lens in question assemblies tend to be very similar:
http://forum.mflenses.com/pentacon-auto-2-8-135-partial-disassembly-and-cleaning-t9836.html

Last edited by Not a Number; 11-18-2012 at 11:29 AM.
11-18-2012, 01:48 PM   #26
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Thanks for the old "let me google it for you". I will take some time and read it all
11-18-2012, 02:17 PM   #27
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QuoteOriginally posted by kcobain1992 Quote
Thanks for the old "let me google it for you". I will take some time and read it all
Works every time!


Steve

(Google provides somewhat different results depending on language and region and even search history...)
11-22-2012, 02:37 PM   #28
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I am on the edge of a complete fail with this 28/3.5. I said to myself, "there's no way the helicoid is bent, it has to have some dirt in the threads that I'm not seeing", so I proceeded to completely degrease and clean it. It has slept a night in detergent, and now, there's something very gritty in it, in spite of me trying to remove all of it with a needle. Obviously I am doing something quite wrong.
11-22-2012, 04:38 PM   #29
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Maybe a high spot in the helicoid thread? Get a good loupe and search the clean threads - both of them - and look for a shiny high spot. If you find one gently scrape the surface where it's shiny with a sharp craft knife blade. It doesn't really matter if a very small portion of the surface ends up 'below' the level of the rest of the thread, it's the high point that's causing the problem. I spent a couple of hours doing this on a lens and cured the tight spot. I have no idea how the tight spot got there, and neither do I care now it's gone.
11-23-2012, 08:27 AM - 1 Like   #30
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I would have used a tooth/fingernail brush, wooden toothpick/matchstick or plastic knitting needle to clean the threads. Nothing metallic that might score the threads. Do you have access to an ultrasonic cleaner?
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