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12-17-2007, 04:36 AM   #1
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EOS lenses on Pentax?

In some other thread I got an idea. Can I use Canon EOS lenses on Pentak K100D body? Does is make sense? Not that I'm gona buy some EOS lenses. I just got some old ones.

As I read the post :https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/16441-modify-c...-fit-k10d.html

I don't need AF and all the electronics. Would it be possible to use the EOS lense in manual mode?


Last edited by pentagor; 12-17-2007 at 05:01 AM.
12-17-2007, 06:05 AM   #2
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I think this won't work.
1. The aperture-mechanisms are completely different.
2. The Distance between the lens and the sensor (I dont know how it's called in English) ist 45,5mm for Pentax-K and 44,5mm for Canon EF.
12-17-2007, 06:15 AM   #3
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QuoteOriginally posted by 2fast4you Quote
I think this won't work.
1. The aperture-mechanisms are completely different.
2. The Distance between the lens and the sensor (I dont know how it's called in English) ist 45,5mm for Pentax-K and 44,5mm for Canon EF.
But it works the other way around... I wonder how! see this ---> AF Confirm Adapter for Pentax K lenses to Canon EOS - (eBay item 190178987581 end time Dec-28-07 05:38:11 PST)
12-17-2007, 08:15 AM   #4
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This adater allows using of Pentax K lenses on Eos-bodys, not using EF-lenses on Pentax-bodys.

The distance between Sensor and lens in the EF-system is 44,5mm. The K-lenses are built for the 45,5mm of the Pentax-K standard.
EF-lenses are built to fit the 44,5mm, but the PK-mount has 45,5mm. 1mm too much. The focus would be totally wrong.

You are also unable to control the aperture, because PK-lenses getting their aperture-setting on a mechanical way. EF-lenses have only electric contacts for the commands from the body. The motor for the aperture is in the lens.

12-18-2007, 04:07 AM   #5
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With a proper adapter a Pentax lens can be used on Canon body, see this picture (not mine).

Last edited by ddhytz; 06-13-2008 at 09:49 PM.
12-18-2007, 04:27 AM   #6
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ddhytz, Is this a crime scene photo? Should be.
12-18-2007, 05:55 AM   #7
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I guess it really depends on how much modification you are prepared to do.

A long time ago I looked at converting K mount lenses to KA mount. Although it was possible, the biggest problem I encountered was the difference in how apatures worked.

on K mount lenses the diameter is changed linear to the movement of the apature lever, on KA mouont it is the apature area, not diameter that is linear with movement. as a result, althoug the modification worked, exposure was off.

I am not sure on the canon lenses how this would behave.

Additionally, you woud need to remove 1mm from the lens to get the mount in the correct spacing to the sensor. (not an easy task, unless you either have a milling machine, or there are removable spacors in the cannon lens. I can envision having to take some material off the mount plus some off the lens to get the distance.

The best option might be to get an old teleconverter (actually 2) and experiment with modifying it to put a cannon mount on one side to receive the lens, and a pentax on the other side to mount into the body. You may be able to account for the difference in distance easier there, BUT, you will still have to deal with the apature coupling, and youy would have double the focal length, which you may not desire.
12-18-2007, 05:58 AM   #8
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I used to use all of my M42 mount lenses on my 20D and 300D when I shot Canon. Used to get ragged on big time by all the hardcore Canonians, lol... I was told it was a "sin". All I know is quite a few were every bit as good, if not better, then my L glass.. i.e. Jupiter 200mm f/4, Novoflex 400mm f/5.6, Vivitar 28mm f/2.8 (actually a rebranded Kyoe Schoji), Practicka-Travegon 35mm f/3.5 R A.Schacht Ulm (rebranded Zeiss), Vivitar 135mm f/2.8 Close Focusing (Komine), Yashica Yashinon 200mm f/4, and Tamron 135mm f/2.8. I only had the normal adapter though, not the AF confirmation one as they didn't have it out at first then it came out but was around $100, and I was getting ready to jump ship away from Canon, so I saw no need to buy it.

As for using Canon lenses on a Pentax, I believe it could be done, but not just with an adapter. I believe you would need to do a permanent swapping of mounts. I have seen folks convert L glass over to Nikon mount. I have converted non-K mount glass to K mount, so I am sure it could be done somehow, but definitely not easily!

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