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09-19-2012, 06:03 PM   #1
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Pointing out some incompatibilities between Pentax and Zenit M42

Hi, I know this has already been discussed before (hell, even I did), but I feel the topic didn't get quite as much attention as the Ricoh pin got (perhaps not that many Pentax and Zenit users).
The problem is twofold: first, SMC and S-M-C Takumars (more precisely, any lens with coupling for open aperture metering) can get stuck on Zenit M42 bodies, because the latter have a different M42 mount, bolt on the body with 4 screws. The SMC Takumars, on the other hand have a small pin that was intended to keep folks from switching the lens from Auto to Manual on their Spotmatic F/ES/ESII. On older bodies, that small pin would have been pressed by the mount and the auto/manual switch would be unlocked. Not on the F though, which featured a new mount, with a groove so that the small pin wouldn't get depressed, putting the lens in manual mode and fooling the camera's meter.
The smart Pentax engineers, combined with Zenit's smart engineers, produced an incompatibility on an universal mount, and many dramas that you can read by simply googling "takumar zenit". Yes, Pentax never really cared about third party compatibility, they repeatedly said in the user manuals that you shouldn't use any other lenses except Takumars on Pentax bodies and Pentax bodies for Takumars.




On the other hand, there's another problem that seems to be less well documented. This one is with respect to using certain non-Pentax lenses, such as Carl Zeiss Jena or Helios 44M on the Spotmatic F/ES/ESII. Other threads on the topic can be found here. The stop-down pin on these lenses seems to get stuck in the levers inside the camera's mount. It is not as dangerous, because the pin can be depressed through the shutter opening, but it still is a very big inconvenience.

It would be helpful if you spread out the word about these facts before anyone destroys their pieces of equipment like I did out of negligence.


Last edited by kcobain1992; 09-19-2012 at 06:10 PM.
09-20-2012, 12:40 AM   #2
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QuoteOriginally posted by kcobain1992 Quote
The stop-down pin on these lenses seems to get stuck in the levers inside the camera's mount.
You are going to have to explain this one to me. The stop-down pin on my Helios 44M is in exactly the same position as the pin on my Super-Tak 55/1.8 and all of my Vivitars in M42. The link you supplied refers to the collar that is present on certain CZJ lenses with pre-set apertures.


Steve
09-20-2012, 09:32 AM   #3
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Yes, I know the other thread I linked to described a different lens, but the problem lies with the body and the aperture sensing lever. On my Helios 44M, the stop-down pin is either too long, or not rounded enough at the tip, because it hits the camera's lever. I have uploaded a video to demonstrate the issue. In fact, at a closer inspection, it seems to me that there is just a little slack (about 1mm) when pressing the pin, during which the aperture isn't closed at all. In fact, if I could find a small enough piece of something to fill that space, the pin would more than likely retract enough to clear the lever.
09-20-2012, 07:29 PM   #4
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QuoteOriginally posted by kcobain1992 Quote
Yes, I know the other thread I linked to described a different lens, but the problem lies with the body and the aperture sensing lever. On my Helios 44M, the stop-down pin is either too long, or not rounded enough at the tip, because it hits the camera's lever. I have uploaded a video to demonstrate the issue. In fact, at a closer inspection, it seems to me that there is just a little slack (about 1mm) when pressing the pin, during which the aperture isn't closed at all. In fact, if I could find a small enough piece of something to fill that space, the pin would more than likely retract enough to clear the lever.
IMGP6096 - YouTube
I watched the video and it occurred to me that the aperture actuator on the body may not be in the retracted position. While the actuator is ramped, and MAY allow a lens to be mounted/unmounted when the meter switch is turned on, it is not designed to be used that way. The first thing I was taught when I first got my Singlex TLS back-in-day was to reflexively flip the meter switch before loosening the lens.

Funny that your Helios 44M is like mine in that the pin does not actuate the diaphragm until almost fully depressed. This is very different than my other M42 lenses.


Steve

09-23-2012, 11:35 PM   #5
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It is. It doesn't hit the actuator, it hits that extra top lever that actually slides.
09-24-2012, 01:12 PM   #6
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QuoteOriginally posted by kcobain1992 Quote
It is. It doesn't hit the actuator, it hits that extra top lever that actually slides.
Ok...yours must be a little different than mine. Mine is virtually identical to the Pentax product in position and depth.


Steve
10-28-2015, 09:40 PM   #7
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Old post but just supporting using feeler gauge to depress smaller button on SMC Takumar lens. I used a 0.05mm gauge. Easy to locate the problem spot. Tapped feeler gauge with tiny hammer so it rode over button, then unscrewed.
Have now written on Zenit EM mount "No SMC lens". Hopefully I never do that again!
cheers
bb2
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