Today it happened. I came home from the camera store with a Toyo 45A, Schneider super angulon 8/90 MC which i believe is from '80s, a polaroid back and a 6x9 roll film back. And a bunch of 9x12 holders, 4x5 still have to be bought. What do you think?
Now the polaroid back I have is rather old looking and it says just "POLAROID 545 LAND FILM HOLDER" on top of the instructions. Is this suitable for readyloads?
You can use Readyloads and Quickloads in a Polaroid holder, but it doesn't have the pressure plate that the Readyload and Quickload holders have, so you may have some film flatness issues.
There are a couple of really good articles about all the 4x5" filmholder systems covering compatibility and other issues at www.butzi.net.
As David pointed out. You can use both in them. However, I have only used Fuji QuickLoads in the Poloroid holder, not the Kodak Readyloads. While I didn't have any problems with the QuickLoads, I soon went to using a Fuji Holder instead (which has issues of its own); it is easier to use than the Poloroid holders (not like they are really difficult), smaller and lighter than the Poloroid.
The film flatness concern with the Polaroid holder is really more of a theoretical problem than one in real life. I have never heard of anyone getting an unsharp images with any of the pre-loaded films in the Polaroid holder. I usually recommend them because they will take the Kodk, Fuji, and Polaroid instant films and function as a universal holder.
I've never used readyloads but I've the quickloads in my polaroid holder and the results have been excellent! Generally I stay away from the ready and quickloads and use sheets due the cost.