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01-22-2012, 06:17 AM   #1
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Where to measure canon fd flange focal distance?

So what started as an easy project turned into a hard one (I guess I should expect that modding lenses). The idea is to take a canon fd teleconverter, and convert the rear mount to k mount. I then have an adapter that gives infinity focus on any canon fd lens (and unfortunatlly doubles it too). If it works with the 2x I am using I will try it with a 1.5x teleconverter. This may be a very complex and difficult project (or maybe not, I guess I'll see).

So before I spend all the time trying it, I'm wondering where the flange focal distance is measured from on a canon fd lens. If you look at the attached picture, there is a stepped mounting face starting right at the top of the threads, and then there is the center hub portion (you can see a screw hole in the side of the part that I am calling the hub). That hub will not clear the lugs on the camera body. With a lens hand held to the camera, I can only focus out to perhaps 1-4 feet depending on the lens (I have a couple of canon lenses). That is at shorter focal distances. At longer focal distances one lens focused out to more like 10 feet.

Is the flange focal distance on canon fd measured from the back face of the portion I am calling the hub, or from the stepped mounting face area? Basically I can make that entire hub portion go away setting the lens back 5mm give or take (depending on how the stepped face area mates up with the m42-k adapter). I gain back 1mm give or take for the thickness of the adapter but I should still be in the ballpark of loosing the 3.5mm I need to, right? Does that hub area even mate up on a canon camera or come into play with the flange distance or does it just fit into the camera and the flange distance goes from the stepped face?

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01-22-2012, 08:51 AM   #2
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Join Date: Jul 2010
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The registration distance of the lens or adapter is due to the optics of the lens so you may just have to
move the inner glass elements closer to the Camera.
I don't know how that one is made but the Off Brand ones I have all have an assembly with long threads and a stop ring that makes them
Just might save you having to cut anything.
If you do it has to be on the Camera side of the adapter and not the lens side.

Good Luck
01-22-2012, 09:29 AM   #3
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Original Poster
This one is not adjustable or threaded where the lens assembly attaches to the body. it slides into place and is held by set screws. Just to be clear, this is a teleconverter. the idea is to have it k mount on the back and canon fd mount on the lens side with infinity focus for canon lenses. even if i could figure a way to move the glass back some, that would move the glass closer to the camera, but would also move the glass further away from the lens that would be mounted to it. Wouldn't that cause a problem?

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adapter, camera, canon, distance, distances, fd, flange, hub, k-mount, lens, pentax lens, portion, slr lens
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