1. 135mm vs 150mm for 4x5 negatives. I'm guessing the differences are subtle, but can someone compare/contrast the two for me. 2. I got an Omega D-II, with just a flat lens board for my small format stuff, but not the little board that lens mounts too, which attaches to that board. I've never mounted an enlarging lens to a board like this. Is it the same as mounting a large format lens? I'm not seeing any refernces to the word "Retaining flange" on the lenses that I'm looking at on eBay. Do they mount this way (where I could build my own boards to attach to the big boards), or do they screw in directly onto the smaller board requiring me to find an actual little board?