So I have an odd lens and I was putting it up for sales since I couldn't use it: http://www.apug.org/forums/forum379/82622-fs-rodenstock-150-5-6-apo-sironar-n-35mm-rear-end.html As you can see from the replies, someone suggests that perhaps a 100mm/105mm Rodenstock rear elements is on it, and looking at the photos from B&H: http://www.bhphotovideo.com/bnh/controller/home?O=&Ntt=rodenstock+lenses it certainly looks like it's possible. Another person says it looks just like the one he has on his Crown. So for now, I have withdrawn the lens from sales so I can find out more about it. **** I am totally a newbie to LF. I presume there are some ways to mount the lens on a board and then at least find out what the imaging circle size is and whether it can focus to infinity or whether it can focus at all. If someone can send me some pointers, I'd appreciate it. Thanks.