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?