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06-02-2010, 11:15 AM   #1
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M42 auto-aperture pin dilemma

I posess more than a few M42 lenses. I use various M42-PK adapters to put them on K-mount bodies. These lenses have various means of controlling the aperture: some are presets or totally manual, some have a aperture pin and an A/M switch, and some only have the aperture pin. Let's call these types M42-P, M42-M, M42-AM, and M42-A. The preset, manual, and A/M lenses allow manual aperture control on all M42 and PK bodies. But M42-A lenses only provide aperture control on M42 bodies that support stop-down automation.

I have so far found only two ways to use M42-A glass on my PK bodies: either wide-open, or with the aperture pins superglued down. Duct tape does not hold the pins down. I've glued a few lenses. Alas, acetone (nail-polish solvent) does not dissolve the glue. I've been told that strong UV light will dissolve it, but I don't have a source. So these lenses seem to be permantly 'fixed', lowering their usability and value.

I still have some M42-A's that I haven't glued, and I'd rather not. Does anyone here have a reversible method for securing aperture pins? Thanks.

06-02-2010, 11:21 AM   #2
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QuoteOriginally posted by RioRico Quote
I still have some M42-A's that I haven't glued, and I'd rather not. Does anyone here have a reversible method for securing aperture pins? Thanks.
I take off the mount and place a piece of cutip straw to keep the pin depressed. It only takes a few moments to do(5 mins. or less) and is completely reversible afterward. Let me know if you'd like a photo of what it looks like.
06-02-2010, 11:29 AM - 1 Like   #3
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I usually use pen ink refill insert tubes to shorten the pin. Don't have elaborate instructions on this but hopefully these few pictures give you a clue


I was naive and inexperienced at first and I bent the pin in the process and I later resurrected the bad attempt with rubber band to tie the aperture mechanics as if the pin is pressed down all the time

06-02-2010, 11:35 AM   #4
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There is an adapter with an inner flange to hold the pin in (Pentax never did this, as they had the A/M switch, but Contax/Yashica has the flange in theirs).

Manual Focus Lenses :: View topic - Pentax-k /m42 adapter with inner flange

06-02-2010, 11:36 AM   #5
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Not all pin and the accompanying mechanics in stop-down are alike, I ran into another case that I need to use longer insert and flip the pin to the opposite side with the same goal to depress the pin permanently


Thanks,
Hin
06-02-2010, 11:42 AM   #6
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QuoteOriginally posted by Nesster Quote
There is an adapter with an inner flange to hold the pin in (Pentax never did this, as they had the A/M switch, but Contax/Yashica has the flange in theirs).

Manual Focus Lenses :: View topic - Pentax-k /m42 adapter with inner flange
Yes, that is one other solution. I have a copy of the adapter from Alex (hk300 in mflenses).









The extra inner flange will depress the pin



more in M42 adapter for auto-mount m42 lens


The adapter works fine to a certain degree if your lens is small. With longer and heavier lens, I find the adapter not locking the lens securely in place. The adapter has its value but like other 3rd party adapters, the material and build is not as good as the genuine Pentax adapter.

Thanks,
Hin

Last edited by hinman; 06-02-2010 at 01:47 PM.
06-02-2010, 12:03 PM   #7
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I like hinman's solution #1 the best, and I have used it on both a lens and a tamron adaptall to M42

as for super glue, isocynates they break down (slowly) with heat and alcohol (not th ekind you drink)
06-02-2010, 01:40 PM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I like hinman's solution #1 the best, and I have used it on both a lens and a tamron adaptall to M42

as for super glue, isocynates they break down (slowly) with heat and alcohol (not th ekind you drink)
There is another issue with isocyanates...they will frost/haze things like focus screens.


Steve

06-02-2010, 03:20 PM   #9
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QuoteOriginally posted by stevebrot Quote
There is another issue with isocyanates...they will frost/haze things like focus screens.


Steve
not just that, anything that allows the vapors to condense, like lens elements etc.

but that is during the cure phase not, at least as far as I know, after cured.

But as I said, i use the pen refil method myself and don't use super glue on photographic equipment any way.
06-04-2010, 11:59 AM   #10
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Thanks for the suggestions. I'd rather not do surgery, so the inner-flange adapter sounds best. Ah, another quest...
06-04-2010, 12:04 PM   #11
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Thin magnet strip?

Or the infamous aluminum tape?

On second thought, forget the magnet. It could fall off and fall in your body.
06-04-2010, 01:36 PM   #12
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Why not the handyman's best friend, duct tape. Perfect for all uses except fixing ducts.
06-04-2010, 02:30 PM   #13
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QuoteOriginally posted by Ira Quote
The infamous aluminum tape?
QuoteOriginally posted by boriscleto Quote
Why not the handyman's best friend, duct tape. Perfect for all uses except fixing ducts.
I tried both. No way, Jose. Firm pressure is required, like S&M play. But no whips.
06-04-2010, 02:42 PM   #14
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I work with a mechanical engineer, and I'll ask him about this next week.

It might be something simple like permanently epoxying an itty bitty standard model/hobby shop item, a post for example, and a thin flat piece of tin/other material with a hole that the post goes into that allows the piece to rotate 360 degrees, so you push the pin down and rotate the piece to hold the pin down.

Am I explaining this right? I'm trying to think of an analogy, but can't come up with one.

Last edited by Ira; 06-04-2010 at 02:48 PM.
06-04-2010, 02:44 PM   #15
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QuoteOriginally posted by boriscleto Quote
Why not the handyman's best friend, duct tape. Perfect for all uses except fixing ducts.
I hate duct tape and only use duck tape.

HAH!!!!!!!!!!!!!
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