I received a Voigtlander Heliar today that most likely comes from a Bessa 66. To be precise, it is a Heliar 7.5cm F3.5 in a Compur shutter. So far nothing special, but when I wanted to unscrew the lenses from the shutter I noticed that the front element could rotate to zone focus. I knew that this can be done with Tessars, for example, but not with a Heliar.



To see if this also works well in practice, I put the lens on a lens board to view it on the focusing screen, with the following results. When the element is fully rotated towards the shutter, the lens seems to work well, but when I unscrew it, the corners became blurry (visible on the focusing screen). This made me wonder if this is really a Heliar and not a Tessar or something, but the structure is the same with 5 elements in 3 groups.

Does anyone have more information about this? I also don't know what this principle is called exactly, so I haven't found much online yet. I'm curious if this really works well, I'll see what can be seen on some film coming weekend.