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08-31-2011, 10:02 AM   #1
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M42 "U" mount/universal thread mount question, please :)

Hi, all! So...I really tried to do my research before buying an M42 lens (and before bugging you kind folks), but, I took a chance and got something I'm not 100% about. The lens I just bought (literally minutes ago and still days away from being delivered still, lol) says it us for "universal thread mount cameras" (it's a Vivitar, Komine series, incidentally). It was one of those M42s not made specifically for Pentax, but certainly Pentax compatible (though it says not with the ES series). It says it has automatic diaphragm control (which I *think* could be a potential red flag, from a reference I saw somewhere) and I believe I can see a pin in the picture. I've read all the horror stories and warnings about things getting stuck. I did just recently purchased one of these cheap but seemingly effective Fotodiox M42 adapters -- effective based on reviews, that is, as this will be my first chance to try it, haha! I'm also not handy with a dremel (yet!) and **really** don't want to even attempt any DIY shenanigans at this point. So...on a K20D, will this puppy work with the adapter out the gate or will that pin need to be sanded down and/or are there any flanges I need to be concerned about? If someone could kindly let me know, I would be most appreciative. As I said, I did do my research and have learned a lot about using M42 lenses, but, there's a lot less documentation on this U mount mount (is that redundant? lol). Thanks so very much in advance! :-)

08-31-2011, 10:06 AM   #2
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Yes, it should work. The pin presses against the mount (to let the lens know that the lens is on a camera) and activates the auto diaphragm. However, you will have to put the lens in manual mode when using it on your k20, as the lever that would normally stop the lens down simply isn't there

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

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08-31-2011, 10:47 AM   #3
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Oh, thank you so much, Adam! I wanted to have the full fun and enjoyment of anticipation for the lens to be delivered and now I can! I use all full manual settings all the time, anyway, so that will not at all be a problem for me. Thanks mucho again! :0)
08-31-2011, 01:08 PM   #4
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The name U or Universal Mount was AFAIK used by marketers who didn't want to name specific camera brands like Praktica or Pentax, and who may have thought that M42 sounded too nerdy / technical for naive customers!

Not all U|P|M42 screwmount lenses are created equal, not even those with auto-aperture pins. There are these types:

* Some have no pin and thus won't automatically stop-down.
* Some have a pin but only stop-down in supporting M42 cameras.
* Some have a pin and an M/A switch, for Manual|Auto operation.
* Some few have two pins; we can discuss those another time.

A no-pin M42 will work in your dSLR in Av mode, as will an M/A lens with the switch set to M. A switchless auto-only M42 will only shoot wide-open on your dSLR unless you glue or jam the pin down, which can reduce resale value. I can use such an auto-only on my M42 film cameras but I avoid them on my K20D. Just be aware of the limitations: no-pin or M/A lenses are fine, auto-only can be a pain. Good luck!

09-01-2011, 12:36 PM   #5
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Thanks RioRico for the additional great/incredibly useful info! Will save all you wrote for future reference, actually. I guess all I can say is...ruh-roh! Sounds like it may not be as breezy as I had hoped ;-) "A switchless auto-only M42 will only shoot wide-open on your dSLR unless you glue or jam the pin down" -- that is my biggest fear, at this point, especially because the box says "automatic diaphragm control." I can't tell from the pix if there are any switches on the barrel of the lens anywhere. Guess I'll have to wait until it arrives. It says on the box: "Vivitar SL Series: Pentax (Non-ES Series); Mamiya/Sekor TL, DTL Series; and other Universal Thread Mount cameras." Anything providing any additional clues there? ;-) It arrives Saturday, so I shall just be patient and hope for the best. And, if I can't play with it, I have a Sigma Mini-Wide II on its way to me, as well (arriving next week, I'm hoping), so, it will be a lovely consolation prize My LBA has barely just begun...but I think it'll be a glorious affliction to contend with =)

P.S. Thank you soooooo much again Adam and RioRico for all the awesome, friendly help!
09-01-2011, 06:04 PM   #6
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QuoteOriginally posted by fleurdelis Quote
"A switchless auto-only M42 will only shoot wide-open on your dSLR unless you glue or jam the pin down" -- that is my biggest fear, at this point, especially because the box says "automatic diaphragm control." I can't tell from the pix if there are any switches on the barrel of the lens anywhere. Guess I'll have to wait until it arrives. It says on the box: "Vivitar SL Series: Pentax (Non-ES Series); Mamiya/Sekor TL, DTL Series; and other Universal Thread Mount cameras." Anything providing any additional clues there?
I *may* be wrong here, but I *think* the Pentax ES Series lenses had a second pin, so a non-ES lens is no problem. I *know* that those Mamiyas were one-pin M/A lenses. And I've just looked as some pics on eBay and I see Vivitar SL lenses with M/A switches visible. So you most likely have a winner there!
09-02-2011, 11:10 AM   #7
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Coolness! Sounds optimistic. Thanks for your legacy lens sleuthing skills Sherlock! ;-)
09-02-2011, 08:44 PM   #8
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Well, Adam and RioRico, it arrived a day early and I am happy to report it worked with my Fotodiox adapter swimmingly! It did have the switch, as well, so you were right, Rio! The pin gets pushed down when it goes onto my camera body and all functioned fine on full manual settings. Here are a couple of quick test shots. Be kind. I am relatively new to all this. Trying to learn the hard with all manual exposures all the time so that once I master it, auto anything will be a breeze if I'm in a pinch Hope to play around with this lens some more soon Take care, ya'll, and thanks again. Thought I'd update this post with this final info so that anyone else looking for the same answer would find out how it all worked out in the end

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Last edited by fleurdelis; 09-02-2011 at 10:09 PM.
09-02-2011, 08:47 PM   #9
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May I ask, if anyone knows, if there is anything I can do to optimize images for this particular site? Is posting a png better, for instance, or a certain pixel dimension? Thanks!

Last edited by fleurdelis; 09-02-2011 at 08:57 PM. Reason: may have unintentionally sounded rude :(
09-02-2011, 09:01 PM   #10
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QuoteOriginally posted by RioRico Quote
I *may* be wrong here, but I *think* the Pentax ES Series lenses had a second pin, so a non-ES lens is no problem. I *know* that those Mamiyas were one-pin M/A lenses. And I've just looked as some pics on eBay and I see Vivitar SL lenses with M/A switches visible. So you most likely have a winner there!
The second pin is more of a square lug on ES/ES II and Spot F enabled lenses. It allows those bodies to work with open aperture metering supported by those bodies. Interestingly, Adapall and Adaptall 2 lenses can be used on those bodies with that feature with the Tamron mount specifically for them.
09-10-2011, 01:19 PM   #11
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Thank you very much, Blue, for that additional helpful reference info. With always scoping out lenses, I'll be tucking that away!
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