A Heliar with an adjustable front group?

[RockAndRolf]

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.

https://live.staticflickr.com/65535/51588122257_ba3703d57e_w.jpg (https://flic.kr/p/2mAEBrK) https://live.staticflickr.com/65535/51589171648_2cf9061458_w.jpg (https://flic.kr/p/2mAKZoG)

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.

[Nodda Duma]

In my humble opinion that seems like a hack job by a previous owner.

[Dan Fromm]

Oh. Bessa 66. Oh. Front cell focusing, not unit focusing.

[J. Patric Dahlen]

Yes, there are front cell focusing Heliars. The Heliar is a modified triplet after all. You can also find it on the Voigtländer Brillant.

Cameras with front cell focusing lenses were cheaper to make and mostly aimed at amateurs, so putting Heliars on them made the cameras maybe a little too expensive for most amateurs, and if you could afford a Heliar-equipped camera you probably could afford a unit focusing one. I think that's why you don't see front cell focusing Heliars that often.

What's the size of the focusing screen you used? The image circle would be larger than 56x56mm (6x6) and less sharp the farther from the centre you get. And it's possible that the focusing scale isn't in the correct position.

[RockAndRolf]

Thanks for the information, this sounds quite logical indeed. I had already assumed that the front element was not officially part of it and that it was more the result of tinkering, as Nodda Duma already indicated. I am currently making a recessed lens board for the intrepid 4x5 to see how far the image circle can be stretched. It seems like a nice angle of view for 6x9, but by then expect dark soft corners. Since he only gets about 50 degrees sharp and that's almost 68 degrees diagonally. As soon as I have pictures I will post them here.