The helicoid solution is a smart one, I am thinking about a Crayford
I was looking for a shutter for a DIY medium format camera and found this forum and your posts. As a machinist I can really appreciate your excellent work. Looking at your posted pictures I saw a Computar lens. I may have this lens. I have an optics bench and fiddle around with optics. I bought two Computar lenses from Surplus Center so I could make a camera. You say that your lens needs to be used with a bellows. Though I want to make a camera with a bellows I would like to know why this lens needs to be used with one. Any advice you can give about where to start looking for info about a DIY camera is greatly appreciated. And once again, great work on your DIY camera.
The Computar 1:16/105~150 needs a bellows to be fully functional because it is a variable focal length lens, and its internal scroll adjusts that.
So the focus has to be adjusted at each focal length, needing the bellows, or a helicoid behind the lens.
It should also be possible to use the lens as an approximate fixed focal lens (eg 135 mm) and obtain focus ability by just using the internal scroll.
So far I am using the lens on the 4x5 Speed with the rollfilm back and using the focal plane shutter. I leave it at 135mm to match the view finder and rangefinder.
I think the lens is pretty good, although i have not used it much.
Here is a photo with it on the Speed, with a 67mm UV filter and an aluminum hood.
At 135mm, note that the lens image circle does not quite cover the RH/8 frame.
Out of camera image (Fuji 400, home processed C41)
Here is a heavy crop of the above which is still reasonably sharp even at 22 inch width on the monitor.
To help with your camera design, here is some data of the Computar from my day book (measured, not calculated):
The register is the rear surface of the lens cylinder which is bolted directly onto a heavy aluminum lens board for the Speed.
At FL= 105 mm the distance from register to film plane at infinity focus, is approx 135 mm at infinity
The focus throw (front standard extension) to focus from infinity down to 5 metre ( 15 foot) is approx 1.6 mm (0.063 inch)
At FL= 135 mm: focus throw :2.4 mm (0.093 inch)
At FL= 150mm register: approx 150 mm at infinity
The focus throw: 4.75 mm (0.187 inch)
So it should be easy to machine a nice helicoid to mount the lens on.
I had the bright idea to allow wider apertures than the fixed f/16. I made a prototype stop to attach to the front of the lens but even f/4 was useless by vignette.
Changing the fixed aperture requires dis-assembly. Then I realized that even at f/16 the image on the ground glass is bright enough to focus fairly sharply.
Anyway I just scale focus it.
Good Luck with your camera!
Nice....I have a secret desire to make something similar out of a LF lens and a 6x12 back. Nicely done.