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02-11-2018, 11:51 AM   #1
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Spotmatic F: non-Pentax lenses won't mount

Hello everyone,

Besides old-but-gold S-M-C Takumars, I have a few M42 lenses from other manufacturers. I wanted to try them on Spotmatic F, but it seems not every one of them would screw-in fully; some lenses just 'bounce off' something after few screw motions and the camera won't let them go further.

Preset/non-auto pin lenses work fine. Some of the auto-pin glass don't. I tried with Auto Mamiya/Sekor 135/2.8 - works fine, but Auto Mamiya/Sekor 55/1.4 will not mount (these are not SX-type, but older TL/DTL). Rollei 85/2.8 won't mount either.

Does anyone know if it is the case with all Spotmatic-Fs (and maybe other open-aperture metering bodies, like ES II), or do I have some sort of a defective model?

All the best

02-11-2018, 03:20 PM   #2
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Are you sure the lenses that won't mount are M42? They could be T-mount which is also a 42mm diameter, but a different thread.
02-11-2018, 03:40 PM   #3
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I just checked the Mamiya 55 1.4 on my F, and you are right. The rear element is too large and extends deep enough to interfere with the added linkage in the F that detects the aperture setting. That lens does work well on. The Spotmatic and Spotmatic II and is a very good lens.
02-12-2018, 05:53 AM   #4
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QuoteOriginally posted by MarkJerling Quote
Are you sure the lenses that won't mount are M42? They could be T-mount which is also a 42mm diameter, but a different thread.
Seems the most likely explanation to me.

02-12-2018, 08:28 AM   #5
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Most likely, there's a rear-element that extends too far, or some other aspect of the lens that is larger than the M42-ES variant that the Spotmatic F uses.

Pentax sometimes had its own compatibility problems, as there were some pre-Spotmatic M42 bodies that couldn't mount the 50/1.4 lens. With the same model number, only the later variant of the body could use the 50/1.4 lens.

As great as the M42 mount is in terms of diversity, there are bound to be issues. If you want to mount any M42 lens, you're best off using a body that doesn't have the auto-aperture lever.

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