Before I bought my 4x5 enlarger I had to use my 8x10 enlarger. I really didn't want to spend the money on a 4x5 carrier for the enlarger (think several hundred bucks). Thus, I looked at a few pictures on the web and made a mask out of acrylic. It was actually pretty easy to make. The acryllic pieces replace the glass in my 10x10 carrier. They both have a 3 13/16 by 4 13/16 hole cut in the middle. I had a nice guy at the university where I work cut them on his laser cutter. They've worked like a charm. However, now I have a dedicated 4x5 enlarger. Mostly because I couldn't afford a pin registered carrier for the 8x10. What negative carriers do you need for your omega? I have several that I'll never use.