<p>John, these where not really unique for the Summitar. At least the Steinheil LTM lenses (Orthostigmat 35, Culminar 135) also used them. They must have been quite popular. Even in the early 70s, when I started with an old Leica IIIb, every photoshop in Stuttgart/Germany had some of them in a drawer. And when they wanted to cleanout the drawer, you could buy them for 2 DM (about 35 US-Cents at this time). Today they are more than scarce.</p>