I just got around to mounting the Protar and the Syntor in boards for my 8x10 and, now that I can measure exactly, the Protar is a 600mm. The Syntor, even with stopping down, was leaving the corners very soft and swirly. I couldn't believe that was correct and figured an element had been reversed in its past. The front and rear inner elements had the same thread and were close to identical but I tried swapping them first with no effect. It had to be an outer element and I managed to slide the rear one out of the mounting (it hadn't moved when I originally cleaned it). I reversed it and that did the trick. Tomorrow, I'll burn some silver with them and a 420mm Dogmar and a 475 Rapid Rectilinear in a mailing tube mount (and an old 300mm Dagor as a benchmark). So, if you happen to have an old Syntor and would like a portrait lens with a very sharp small center fading to very soft and swirly corners, just reverse the rear element.