I have a Bronica ETRS and have wanted to adapt other lenses but, as you know, it is difficult because of how the system works. I was considering using a 75mm lens with the glass removed and the alternate lens adapted by use of a filter ring or lens cap onto the front of the 75mm lens. In the case of shuttered alternate lenses I considered setting the 75mm on T and then using the shutter on the alternate lens. If anyone has any experience doing things like this I'd like to hear how good it worked, etc. I know, it is easier to use a camera with a focal plane shutter.