Framing with a folding camera with different focal length

Laci Toth · Jul 9, 2020

Hi all,

I have a Bettax 6x9 folding camera with a Compur shutter and a Schneider Kreuznach 10.5 cm lens. As the shutter stopped working entirely within a few days (first the low and then the rest of the speeds) and the repair would be expensive I ordered a new one as I found one dirt cheap. This one even has a lens a Carl Zeiss Jena Tessar 12 cm. My question is how to frame with the longer focal length? Okay I have to experiment but someone might come up with an idea.

Thank you!

Donald Qualls · Jul 9, 2020

A Bettax with a 12 cm lens? I'm pretty confident that's not original. The bed on a 6x9 folder won't extend the lens standard enough to focus to infinity, never mind anywhere closer. That focal length is what I'd expect for a 122 postcard format camera (3 1/2 x 5 1/2 frame)...

wiltw · Jul 9, 2020

The area framed with 12cm FL will simply be 88% as wide and tall as with the original 10.5"cmFL...a bit more 'telephoto'

Donald Qualls · Jul 9, 2020

I think the original lens was a 10.5 cm and the new one is 12 cm, no inches involved here.

Dan Daniel · Jul 9, 2020

Laci Toth said:
Hi all,

My question is how to frame with the longer focal length? Okay I have to experiment but someone might come up with an idea.

Thank you!

Before you worry about framing, you need to worry about focusing. How do you plan to get the extra 1.5cm or so you will need to move the lens forward?

Vaughn · Jul 9, 2020

I would photograph a large grid pattern, note the coverage in existing viewfinder and compare it to what ends up on the negative.

wiltw · Jul 9, 2020

Donald Qualls said:
I think the original lens was a 10.5 cm and the new one is 12 cm, no inches involved here.

I adjusted my reply for cm, not inches.. The 88% (narrower) FOV than 10.5 cm holds true neverthless.

Donald Qualls · Jul 9, 2020

wiltw said:
I adjusted my reply for cm, not inches.. The 88% (narrower) FOV than 10.5 cm holds true neverthless.

True -- though it won't matter, because there's no way a 12.0 cm lens will focus on a Bettax; it's a fixed-standard bed folder.

wiltw · Jul 9, 2020

For benefit of OP, putting 12cm lens in place of 10.5cm lens is similar to putting a 57mm lens on 135 format camera in place of 50mm lens

Laci Toth · Jul 9, 2020

Thanks for all the info! I thought that I can just change the lens like in the case of interchangeable lens cameras and that’s it.
I’ll then only use the new shutter and will use the Schneider lens.

wiltw · Jul 9, 2020

Laci Toth said:
Thanks for all the info! I thought that I can just change the lens like in the case of interchangeable lens cameras and that’s it.
I’ll then only use the new shutter and will use the Schneider lens.

But the problem you can certainly have is that the FOCUSING is different for the longer FL lens, even if the image area in the little window can be mentally 'accomodated' by allowing a little edge for 'crop' due to longer FL. The 10.5cm lens would be 10.5cm from the film plane to be in focus at Infinity focus, and the 12cm lens would be at 12cm from the film plane also at Infinity focus.

Laci Toth · Jul 10, 2020

wiltw said:
But the problem you can certainly have is that the FOCUSING is different for the longer FL lens, even if the image area in the little window can be mentally 'accomodated' by allowing a little edge for 'crop' due to longer FL. The 10.5cm lens would be 10.5cm from the film plane to be in focus at Infinity focus, and the 12cm lens would be at 12cm from the film plane also at Infinity focus.

Okay, so if I take out the 12cm lens and put the 10cm lens in can I use the shutter and will it properly focus? Or every compur shutter belongs to that very lens? Because it seems that the shutter is identical to the previous one.

Dan Daniel · Jul 10, 2020

Shutters come in various sizes, but yes, a Compur #0 should be interchangeable with another Compur #0, etc. For lens elements, that is. Actual mechanical connections, shutter release, location of pins, etc. vary based on final users' desired configuration. So check these things

You'll need to swap over the aperture scale.

Donald Qualls · Jul 10, 2020

If both lenses are in the same size and similar age Compur shutters, you should be able to do what you propose: remove the bad shutter from the front standard by unscrewing the retaining ring, remove the lens groups from both shutters, install the 10.5cm glass into the working shutter, then install the shutter in the front standard. Be careful in the process, as with some cameras (and I don't know the Bettax) it's easy to bend or "rack" the front standard, resulting in effects like a tilt or swing (plane of focus is no longer parallel to the film plane).

If you were replacing the glass in the original shutter, you'd run into the other potential gotcha: two different 10.5cm lenses may have a couple millimeters of difference in focal length. At the factory, this was handled by manufacturing the front standard for the shortest in-tolerance focal length and shimming the shutter to move it forward for lenses with slightly longer focal length. In your case, you shouldn't see this problem -- but do be sure to transfer any shims, washers, or felt rings between the shutter housing and front standard to the new shutter along with the lens cells.

Dan Daniel said:
You'll need to swap over the aperture scale.

And this, too.

Laci Toth · Jul 10, 2020

Dan Daniel said:
Shutters come in various sizes, but yes, a Compur #0 should be interchangeable with another Compur #0, etc. For lens elements, that is. Actual mechanical connections, shutter release, location of pins, etc. vary based on final users' desired configuration. So check these things

You'll need to swap over the aperture scale.

Thank you!

Laci Toth · Jul 10, 2020

Donald Qualls said:
If both lenses are in the same size and similar age Compur shutters, you should be able to do what you propose: remove the bad shutter from the front standard by unscrewing the retaining ring, remove the lens groups from both shutters, install the 10.5cm glass into the working shutter, then install the shutter in the front standard. Be careful in the process, as with some cameras (and I don't know the Bettax) it's easy to bend or "rack" the front standard, resulting in effects like a tilt or swing (plane of focus is no longer parallel to the film plane).

If you were replacing the glass in the original shutter, you'd run into the other potential gotcha: two different 10.5cm lenses may have a couple millimeters of difference in focal length. At the factory, this was handled by manufacturing the front standard for the shortest in-tolerance focal length and shimming the shutter to move it forward for lenses with slightly longer focal length. In your case, you shouldn't see this problem -- but do be sure to transfer any shims, washers, or felt rings between the shutter housing and front standard to the new shutter along with the lens cells.

And this, too.

Thanks for your input!

Donald Qualls · Jul 10, 2020

Be sure to come back and post some results after you get it done.

Laci Toth · Jul 10, 2020

Donald Qualls said:
Be sure to come back and post some results after you get it done.

=)
I’ll be on it!

Framing with a folding camera with different focal length

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