Help me understand this.... I am trying to find a method to focus, without bellows or any movements and helical mounts are not possible (not worth getting into that part)
I beleive a Helical focussing mount simply provides greater distance between the front and back lens sections, which appears is seperated by the shutter. (at least in View Camera lenses) If this is correct, and I am using a 47mm focal lenght lens...and only need focussing between infinity and say 20 ft..... then my calculations say the additional spacing requried between nodal point and film plane is only .3mm. Now, I don't know how this equates to the lens element seperation when focussing with a helical mount? But I assumed it would be close...or at least not much differences, as the helical mounts themselves are not very thick.... So I took a 55mm Rodenstock Grandagon and put it on my view camera.... I focussed at infinity...then tried to unscrew the front element, making seperation between the front and back element. I thought I would be simulating a helical focussing mount. But much to my surprise, even when unscrewing the lens front all the way out, at least 4mm, I noticed the focus point on the gg was not changing? What is flawed here? This would be a very elegant solution.
Possibly I need a longer threaded barrel to screw into, i.e. to create more distance?
Next I thought about shims on the back, as the lens board can't be moved....but this would be cumbersome, as I need shims in the .1mm thickness range, which would be hard to keep them from bending as they would need to fit around a 5x7 back. So I really want to explore this pseudo helical concept as it will be the easiest method to focus in the field as I do have gg to view focus point. And since my focus requirements are so small, I would think there must be some mechanical solution?