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06-06-2019, 08:44 AM   #1
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Spotmatic F Lens compatability

This might be a very silly question, I'm not particularly knowledgeable with these cameras. I have a Spotmatic F and just bought a Pentacon 1.8/50 auto mc, and when I try to screw it onto my body it stops dead about a quarter turn from the correct orientation and as soon as I let go it unscrews itself a bit and is very loose. I know its an M42 body, and it's definitely the M42 version on the lens, and my other two M42 lenses fit the body...

Is it a problem with the lens? My body? Just incompatible? Fairly stupidly I've already started the return process and bought another one from Ebay when I probably should have asked on here first. If this lens is just plain incompatible, could anyone suggest a good alternative that won't break the bank?

Thank you in advance

06-06-2019, 09:03 AM   #2
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The aperture pin gets in the way when it is on auto. Same thing with a takumar even. (I never use these film bodies so I don't have experience here but I have some sitting around.) Solution seem to be put the lens on manual for mounting (and dismounting also) and make sure the pin goes down (gravity can take care of that if the lens is facing downward).

Last edited by vonBaloney; 06-06-2019 at 09:28 AM.
06-06-2019, 09:43 AM   #3
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QuoteOriginally posted by vonBaloney Quote
The aperture pin gets in the way when it is on auto.
Do you have the lens and camera in question? The SP F has a complicated mount; are you saying that the aperture actuator pin is overly long and is fouling the couplings used for open aperture metering?


Steve
06-06-2019, 09:48 AM   #4
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Spotmatic F has a special thing inside it that reads aperture setting on S-M-C and SMC Takumar lenses. This allows for open aperture metering with those lenses. However, the same mechanical assembly gets in the way with third party lenses and their stop down pins.

My auto Mamiya/Sekor 55mm/1.4 and Rollei-HFT m42 lenses won't mount because of that. Solution described by vonBaloney did not work in those cases; maybe it will in yours.

06-06-2019, 09:55 AM   #5
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Thank you so much for the advice, setting to manual for mounting seems to have worked perfectly and it now mounts fine. One thing I've noticed is that the button on the side that stops it down doesn't do anything with this lens, but when I set the shutter speed to B and look through the lens I can see it's getting stopped down correctly for taking photos. This isn't going to be an issue, right?
06-06-2019, 10:10 AM   #6
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QuoteOriginally posted by stevebrot Quote
Do you have the lens and camera in question? The SP F has a complicated mount; are you saying that the aperture actuator pin is overly long and is fouling the couplings used for open aperture metering?
Yes, I have the camera and lens, although I never have used the camera so I don't really know the ins and outs. And no, it isn't too long as far as I can tell (but maybe it is by a micron), but on auto it stays sticking out (with much resistance to being pushed in) and is hitting something and gets hung up. Trying a 50/1.4 auto Takumar had same trouble (which I thought was weird), although not as severe. Putting lens on manual so the pin would recede makes it easy to mount (and unmount -- the Pentacon won't unmount in auto) although once mounted in the correct position you can put the lens on auto and it seems to be fine.
06-06-2019, 10:19 AM   #7
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QuoteOriginally posted by Oscar Velour Quote
Is it a problem with the lens? My body? Just incompatible?
Welcome to the Pentax Forums!

One question, is your lens the "vanilla" version with an uncomplicated M42 mount or does it have electric contacts on the mount face? Those would be fairly obvious and might be fouling the screw holes on the camera if the lens has them. If not, one would normally expect wide cross-compatibility with M42 bodies in general. Your SP F has a rather special proprietary mount that varies in that it has couplings in the mirror box used for open aperture metering with S-M-C and SMC Takumar lenses. The mount face is also rather special in that it has a cut-out "ledge" on the inboard side.

That last might be part of your problem in that the photos of the Pentacon Auto MC 50mm f/1.8 that found show a fairly narrow flange for actual engagement with the body flange that might be allowing the lens to screw deeper into the mount than is proper such that the aperture actuator pin fouls with things that would normally not be in the way.

All that being said, even if @vonBaloney 's suggestion above works, it might be worth checking that there is a slight gap between the edge of the lens body and the mount flange of the camera. If not, the lens flange has nested into the cut-out ledge area of the mount rather than engaging the face. This might be benign or there might be a risk of fouling the mirror at minimum focus distance. (Your lens is known for having closer focus than most and photos seem to show generous intrusion when at its closest focus setting.)

Good luck!


Steve

Last edited by stevebrot; 06-06-2019 at 10:43 AM.
06-06-2019, 10:29 AM   #8
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QuoteOriginally posted by BarneyL Quote
Spotmatic F has a special thing inside it that reads aperture setting on S-M-C and SMC Takumar lenses.
I'm thinking this is the correct answer as to what is wrong. I'm betting on the apeture pin in the lens or somethign else in the lens getting hung up on it. Even with S-M-C and SMC takumars if not seated all the way they will unscrew themselves a bit. With those on my Spotmatic F cameras I know just to tighten them back up all the way and they are fine. However 3rd party lenses I would be a bit more cautious until I knew for sure what was getting hung up.

06-06-2019, 10:34 AM   #9
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QuoteOriginally posted by Oscar Velour Quote
One thing I've noticed is that the button on the side that stops it down doesn't do anything with this lens, but when I set the shutter speed to B and look through the lens I can see it's getting stopped down correctly for taking photos. This isn't going to be an issue, right?
That button should flick the aperture actuation flipper to the engaged position for stop-down metering or checking depth of field; the lens should stop down when the switch is in the up position and be open when it is not.

Do you have the Spotmatic F manual? It provides a fairly poor description of how the button is used, but is better than nothing.

Pentax Manuals | M42 Cameras (PDF password is "Pentax")


Steve
06-06-2019, 10:40 AM   #10
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QuoteOriginally posted by BarneyL Quote
My auto Mamiya/Sekor 55mm/1.4 and Rollei-HFT m42 lenses won't mount because of that.
Can you send me a private message with the details. The section of the homepage article on the M42 mount dealing with compatibility concerns has not been fully fleshed out and any additional information would be helpful.


Steve
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