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01-29-2008, 02:43 PM   #1
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Pentax & Canon Lens Compatibility?

I have a mint Canon FD 500 mirror lens that I've had for about 20 years, and a AE1p body. But I never use film any more.

Can this possibly be adapted to my K10 ?

01-29-2008, 04:00 PM   #2
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Even if you manage to change the mount, you would have to sacrifice the infinity focus.
01-30-2008, 01:19 AM   #3
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Aegisphan is right. Canon EOS mount has 44mm of lense to sensor distance, while Pentax K is 45.5 mm (like M42 screw mount). This is the distance that is required for correct focusing.
01-30-2008, 09:32 AM   #4
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so the lens would only focus up to a certain distance then?

If that's the case, could that distance be calculated?

( I guess I need a better explanation )

01-30-2008, 10:00 AM   #5
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A quick and dirty way to find out:

1. Mount the lens on your K10d (after the mount conversion of course)
2. Pick out a test subject
3. focus to infinity, and set the lens at wide open
4. then stand roughly at the furthest distance next to infinity mark on the lens (like my 31, the furthest next to infinity is 2 meters away).
5. Then slowly move back until the test subject is in focus. That would be distance.

For exact calculation, just read "The Ins and Outs of Focus" by Harold Merklinger:
Download The INs and OUTs of FOCUS
01-30-2008, 11:16 AM   #6
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Lloydy,
I just looked at a photo of the 500mm at the B&H site. It has the lens mount attached to the main unit with screws. It looks like a good craftsmen could easily cut down the mount and attach a K-mount bayonet to it. It would be reduced in lenght by 1.5mm to correct infinity focus of course. There is no diaphraim to be concerned about. It might need a rectangular mask at the camera end to reduce flare. I made a 2X teleconverter with Pentax at the camera end and Nikon female bayonet at the lens end. This allows me to use my Nikkor lenses in preset mode. This is mainly for use with my Nikon Macro lens. I switched to Pentax because of the support for older equipment. Good luck.

Dave

Used Canon | Telephoto 500mm f/8.0 Reflex FD Manual | C218152211
01-30-2008, 12:48 PM   #7
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QuoteOriginally posted by pentagor Quote
Aegisphan is right. Canon EOS mount has 44mm of lense to sensor distance, while Pentax K is 45.5 mm (like M42 screw mount). This is the distance that is required for correct focusing.
I might be mistaken, but I thought the Canon FD mount was different than the EOS mount including in the distance between the lens->film plane distance. Whether an FD mount lens can be modified to a K-mount is another story though.

I'd recommend looking for FD to k-mount adapters and see what comes up.
01-30-2008, 01:05 PM   #8
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FD Registration Distance (RD): 42mm
EF RD: 44mm
K-mount RD: 45.46mm

01-30-2008, 01:16 PM   #9
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QuoteOriginally posted by aegisphan Quote
FD Registration Distance (RD): 42mm
EF RD: 44mm
K-mount RD: 45.46mm
I thought they were different (Though I didn't think the FD's registration distance was shorter )
01-30-2008, 03:15 PM   #10
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Wow! a lens that has actually appreciated in price I paid a lot less than that for it, but maybe over here the price would be less?

I have a scrap Ae1 body, so I might look at getting a cheap Pentax mount and butchering something. I am an engineer with access to lathes and other equipment so this would be an interesting project.

It's a lovely lens that I had some great shots from, and actually my bought it for me so I would like to use it again.
01-30-2008, 08:30 PM   #11
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Lloydy,
I got a great idea for making a new adapter tube. Make it in two peices, where the mount portion threads onto the lens section. Using fine threads, so that you can fine tune the focus at infinity. Then use a set screw to lock it down. I just checked my notes and the FD registration is 42mm, rather then 44mm, so it would be 3.5mm shorter overall lenght.

Dave
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