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06-24-2019, 03:38 PM   #1
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Pentax screw mount lens mirror interference with Canon 7d ?

I have a number of SMC 42mm mount lenses that I have with adapters for my Canon 7d. Any sure way to know what lenses I have will not have interference with the mirror ? I have ruled out my 24mm F3.5 after finding some info online. I would rather be safe than sorry. Thanks!!

06-24-2019, 03:59 PM   #2
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Since the SMC M42 registration distance is 45.46mm and the EF/EF-S mount is 44mm there should be no chance of the rear element of the M42 lens projecting into the mirror box. Just check that the rear element of your M42 lens does not project when it moves through the focus range. But I would assume that if it did it would interfere with the mirror on Pentax bodies anyway.
06-24-2019, 04:38 PM   #3
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QuoteOriginally posted by PJ1 Quote
Since the SMC M42 registration distance is 45.46mm and the EF/EF-S mount is 44mm there should be no chance of the rear element of the M42 lens projecting into the mirror box. Just check that the rear element of your M42 lens does not project when it moves through the focus range. But I would assume that if it did it would interfere with the mirror on Pentax bodies anyway.
Thanks!!! I have tried a few of my longer than wide angle lenses with no issue, but wondered about my 28mm, and my 35F3.5 and my soon to arrive 35mm F2.
06-24-2019, 05:07 PM   #4
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QuoteOriginally posted by JimboWalker Quote
wondered about my 28mm, and my 35F3.5 and my soon to arrive 35mm F2.
I would fit the lens to the adapter (not mounted on the camera) and turn the focus ring through its full travel. If the rear element does not project from the adapter I don't see how it could get near the mirror.

06-24-2019, 05:12 PM   #5
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QuoteOriginally posted by PJ1 Quote
I would fit the lens to the adapter (not mounted on the camera) and turn the focus ring through its full travel. If the rear element does not project from the adapter I don't see how it could get near the mirror.
I just checked a few lenses and some do extend beyond the flange, but have not tried with adapter. I'm surprised my SMC 50mm 1.4 extends beyond.
06-24-2019, 05:55 PM   #6
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QuoteOriginally posted by JimboWalker Quote
I just checked a few lenses and some do extend beyond the flange, but have not tried with adapter. I'm surprised my SMC 50mm 1.4 extends beyond.
Well, the 50mm f1.4 has been known to hit the mirror on some Pentax bodies, so no great surprise for that one...

I thought there were some mods unfortunately common to Canon users that were irreversible... is it an aperture pin thing?

-Eric
06-24-2019, 11:20 PM   #7
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QuoteOriginally posted by PJ1 Quote
Since the SMC M42 registration distance is 45.46mm and the EF/EF-S mount is 44mm there should be no chance of the rear element of the M42 lens projecting into the mirror box. Just check that the rear element of your M42 lens does not project when it moves through the focus range. But I would assume that if it did it would interfere with the mirror on Pentax bodies anyway.
My Westromat 35/2.8, at infinity, would foul the mirror of my Spotmatic:

https://www.pentaxforums.com/userreviews/isco-g-ttingen-westromat-35mm-f-2-8.html
06-25-2019, 12:00 AM   #8
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Here is a list of m42 lenses and canon 5d. Not all canon cameras have this problem but the 7d might.
Compatibility list of M42 lenses on Canon EOS 5D DSLR

06-25-2019, 02:28 PM   #9
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QuoteOriginally posted by swanlefitte Quote
Here is a list of m42 lenses and canon 5d
So there it is definitively. I might have known someone would have the goods. The OP will just have to check on the 7d.
06-25-2019, 06:41 PM   #10
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It appears that the 7d is apsc and not affected. DATABASES *| *Using Contax C/Y Lenses on Canon dSLRs
06-26-2019, 03:29 PM   #11
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QuoteOriginally posted by swanlefitte Quote
Here is a list of m42 lenses and canon 5d. Not all canon cameras have this problem but the 7d might.
Compatibility list of M42 lenses on Canon EOS 5D DSLR
I just checked all of my lenses with a Fotodiox adapter and none of them protrude further than 1/2 mm! Even my 24mm f3.5 only extends about 1mm beyond the adapter!! I feel safe now using them on my 7d. The 5d info scared me. Thanks to everyone! I still think infinity focus is not good with adapters. Midrange and closer is much more accurate .
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