I've been doing some research on projection lenses and there were several manufacturers watching each other very closely. I believe the Radiant is a second generation modified Petzval that would be Gundlach's equivalent to the B&L Cinephor II. At some point, most manufacturers switched to a six element (non-Petzval) design that was fast and highly corrected. For B&L, I think the switch came during the production of their Super Cinephor line. It looks like early Super Cinephors were still Petzval designs, but most of the lenses were the newer six element design. I have a 6" Gundlach (see pic) that preceeded the Radiant--it's a big fat classic Petzval and very large for a 6" lens. I think they were trying to find designs that would allow fast, but smaller lenses.