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07-21-2014, 05:47 AM   #1
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canon lenses on Pentax 645d

Hi does anyone know if you can get an adapter to use a canon lens (ie my excellent 70-300 zoom) on a 645d please? Just an idea :}

07-21-2014, 07:48 AM   #2
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Even if there was such an adapter the lens would not cover the full image circle of the 645d, so you would get extreme vignetting. Maybe I'm missing something but I do not think this would work.
07-21-2014, 07:51 AM   #3

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Do you know if that 70-300 has a large enough image circle to be used on a 645D?
07-21-2014, 07:57 AM   #4
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registration distance is going to be a problem.
  • Pentax 645 70.87mm
  • Nikon 46.5mm - and Canon is even shorter
The physical diameter of the mount is substantially different. The difference in sensor size with the 645 being 60% larger and nearly double the distance away - I see as a problem that will be difficult to solve.

Last edited by interested_observer; 07-21-2014 at 10:49 PM. Reason: for some reason pulled the Nikon registration distance and not the Canon - just noted this
07-21-2014, 08:17 AM   #5
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Forget the image circle unless you are interested in an extreme macro zoom. The registration distance for the Pentax 645 mount is almost twice that of Canon.

07-21-2014, 10:00 PM   #6

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QuoteOriginally posted by greatgable Quote
Hi does anyone know if you can get an adapter to use a canon lens (ie my excellent 70-300 zoom) on a 645d please? Just an idea :}
Simple answer - NO. The registration distance, which is the distance from the mounting flange to the sensor/film plane is smaller for Canon lenses.

This means you would need to mount the Canon lens about an inch (25mm) inside the Pentax 645 mount where it would be hit by the mirror.

Not going to work.


07-22-2014, 07:27 AM   #7

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This thread has a link to a picture of someone who mounted a Nikon 300/2.8 to a Pentax 6x7.

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