canon lenses on Pentax 645d

greatgable · 07-21-2014, 05:47 AM

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 :}

**jatrax** · 07-21-2014, 07:48 AM

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.

tuco · 07-21-2014, 07:51 AM

Do you know if that 70-300 has a large enough image circle to be used on a 645D?

**interested_observer** · 07-21-2014, 07:57 AM

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

stevebrot · 07-21-2014, 08:17 AM

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.

Steve

**seventhdr** · 07-21-2014, 10:00 PM

Originally posted by greatgable

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.

Regards

Chris

tuco · 07-22-2014, 07:27 AM

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

07-21-2014, 05:47 AM	#1
greatgable New Member Join Date: Jul 2014 Posts: 10	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, 07:57 AM	#4
interested_observer Loyal Site Supporter Join Date: Jun 2009 Location: Tumbleweed, Arizona Photos: Gallery \| Albums Posts: 5,707	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

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07-21-2014, 07:48 AM	#2
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	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
tuco Pentaxian Join Date: Jul 2009 Location: Pugetopolis Posts: 11,025	Do you know if that 70-300 has a large enough image circle to be used on a 645D?

07-21-2014, 08:17 AM	#5
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	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. Steve

07-21-2014, 10:00 PM	#6
seventhdr Site Supporter Join Date: Mar 2007 Location: Christchurch, New Zealand Photos: Gallery Posts: 1,440	Originally posted by greatgable 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. Regards Chris

07-22-2014, 07:27 AM	#7
tuco Pentaxian Join Date: Jul 2009 Location: Pugetopolis Posts: 11,025	This thread has a link to a picture of someone who mounted a Nikon 300/2.8 to a Pentax 6x7.