Film Advance system research for DIY Camera

It seems like a simple linkage between the counter mechanism and the winder would solve the problem. (Perhaps with Reset from the shutter...?)f
  • #1
TL;DR Summary
I'm figuring out how to advance a film on a spool and reduce the rotation speed throughout the winding of the film. Because the circumference of the rolled film changes, so does the spacing between the frames if I have a unique rotation for the whole film.
Dear All,

I'm a french professional photographer working on Still Life and Architecture.
As a long time and personnal project I'm working on a 3D printed/Laser cut analog camera that will shoot 6x4.5 frames.
In the end it will be some kind of rangefinder with integrated electronic light measurement, custom lens, custom electronic leaf shutter.
If have been inspired by Panomicron and Cameradactyl with their work on the subject.
This is the start of a multiple year project.

For the first iteration I am designing a simple body with only the rewind mechanism of a 120 film, 16 frames per roll, and a Mamiya Press lens with integrated mechanical shutter. For now I'll be using Range focus and decoupled viewfinder.
For the second I'll be adding a viewfinder.
3rd will be adding a rangefinder mechanism.
4th will be adding the electronic light measurement
5th will be creating an electronic leaf shutter.
6th creating a lens with high-quality manufacturing (like Edmund-optics). (3-5years)

The idea is to have a Camera that is best fitted to my appreciation of photography, that I am able repair and that I fully understand.
You can follow the ongoing work on my instagram @camillelemonnier_

As of my past Architecture studies I have basic knowledges of physics and mechanics and do know how to use 3D designing softwares such as Rhinoceros. Plus I'm super eager to learn.
But as I am not an engineer nor an industrial designer I think this community might help along the way.

As of now, I have worked on the focal flange distance of the lens to determine the exact distance from lens to film and the attach system of the lens.
My first problem to solve is dedicated to the winding mechanism. I intend to use a thumb lever to advance the film so that I have a fixed movement and not worry about film alignment.
My first mechanical question of a long series is:

How do you slow down the rotation of the spool so that you can have the same distance between the frames?
The more I advance the film, the larger the circumference of the roll becomes. Meaning that if I have a unique rotation for each frames, I'll have a expending distance between the frames and then will be loosing a lot of film in the process.

Here's what I've roughly calculated last night:

I based my numbers on physical measurement of the film and the diameter of the roll at different times.
Although my numbers might not be exact from a few microns, the point was made.
If I go down as low as 0.94 turns, I'll be loosing 13,1 cm of film on a 83 cm roll, which is almost two lost frames (vertical 6cm x 4,5cm with 5mm spacing) and the distance between the two first frame will be of 1mm. Theorically I could stay on 15 frames, practically it wouldn't work.

So I have to find a way to reduce the number of turns while the film advances so that I can have a different rotation from frame 1 to 16.
Do you know any mechanical designs that does that?

I've checked the hasselblad film back designs, and well it's pretty perfect, but I want to know if there is any other mechanism that I can be inspired by, or other schematics in other fields or if there is anything simpler. Plus it's really hard to reverse engineer and compile for a 3D printed/Laser cut camera.
Below is an exploded view of the system where I believe group 63 is the mechanism that allows the rotation to slow down at each turn.
And a video that shows the mechanism:

This is just an example, but does any mechanical principles come to your mind concerning a constant reducing speed rotation of the spool and associated gear, without using 16 different gears ?

I hope I made myself clear and that my english is not too bad.
Thank you for the help.
  • #2
Since you are designing this camera from scratch, how about making the take-up spool larger diameter?

That way each layer of the film will be a smaller percentage of the diameter and there will be fewer layers.

There is also the 'continuously variable transmission' transmission approach that is more complex.
  • #3
Why not simply advance the film one picture space repeatedly, and keep tension on the winding reel by a slipping drive?
  • #4
I don't recall if 120 film has sprocket holes, but here is an idea:

In the few 35mm cameras I've taken apart, there are guide sprockets before and after the the exposure area. Often one of these drives a frame counter thru a gear train, -- X-sprocket holes equals one frame.

It seems like a simple linkage between the counter mechanism and the winder would solve the problem. (Perhaps with Reset from the shutter release.)


Suggested for: Film Advance system research for DIY Camera