C-mount (RPi HQ camera) to M39 (Componon-S f2.8) extension tube for 3D printing

[ChrisCph]

First off, thank you all for the very helpful responses.
I’ve been on this forum since 2019 and have eagerly read all of the posts and amazing designs.

@dgalland

Results

Really helpful overview of the calculation. Thank you very much. When extending to (S)16mm I get the following:

I assume these numbers would further change, when needing to capture sprocket holes and optical sound.

@dgalland

The distances are between the film, the sensor and the theoretical focal point of the lens. Add approximately 50mm and to be more precise consult the Componon diagram to have the position of the theoretical center of the object in relation to its front or rear face, 42 mm for the back focal

I don’t fully understand this, and hoping for a bit more explanation. Here’s how I understand how the calculations should be applied, please correct me if I’m wrong:

@dgalland

Note that the helical ring is to determine the length of the tube and therefore the magnification, for focusing we move the entire assembly. I highly recommend a 3-axis micrometer table but it is quite expensive. Certainly quite difficult in 3D printing because it is very sensitive and must be very stable.

I will try to design an extension tube that will work in the same way as a helicoidal ring (if I understand the function of a helicoidal ring correctly), splitting the tube in an inner and outer tube (threaded) allowing the length to vary with X amount of cm/mm by unscrewing the two pieces from each other.
Something like this, but maybe with a custom finer thread than M48 for greater precision:

And then there would at least have to be 2 different top-tubes with different lengths, to accommodate the extension range needed, and probably also 2 additional for 16mm.

I also thought of using a 3 axis linear stage for fine positioning the camera, after seeing the many designs here, but I may start with a 3D printed design of a linear stage, and see how good it works, and if it’s terrible I will have to buy one (hopefully one can be found used, in good condition, and cheaper).

@Manuel_Angel

I share @dgalland 's opinion. Extension tubes and other lens-camera coupling elements are easily and cheaply found in online stores.

Thank you for the links to the various adapters. They are indeed cheaper than I thought. However I really like the idea of making a 3D model which everyone can use for free, and print themselves. Maybe I’m blinded by 3D printing and the expression: “With a hammer in hand, everything looks like a nail” fits me, but I think 3D printing is commonplace today, and chances of knowing someone who can 3D print for you are high. I can also make a version of the tube with a M42 thread, if you’re interested?

@Manuel_Angel

On my device, the distance between the back of the lens (with the tube fully screwed in) and the front of the HQ camera C-mount (without the 5mm ring) is 80mm.

Interesting, as the 80mm is roughly 10mm more than the calculations above. But from the frames you posted hereMy telecine machine - #8 by Manuel_Angel it looks like you are also grabbing part of the perforations/sprocket holes, which would make sense calculation-wise (or is it actually the other way around: capturing sprocket holes requires less length?). Capturing sprocket holes is definitely something I want to allow for with the extension.

@Manuel_Angel

To adjust the entire optical system, @jankaiser had the excellent idea of photographing graph paper

I wish you success in building your film scanner.

Yes I read the post a while ago, and thought it was a brilliant alternative to the “hard to get” (read: expensive) SMTPE test film.
And thank you!

@PM490

I do not have a 3D printer, and what I have designed was printed commercially with machines that have greater capabilities than your typical home printer. With this disclosure, and my very limited 3D printing experience, I would like to offer a couple of suggestions.

• A thicker wall may be needed to avoid deformation in the long tube, and to support the arm of the lens x tube length. If this is already considered in your design simply disregard, again, my hands on printing experience is limited.
• A typical problem of the HQ sensor and long tube requirement, is a good stable support for the assembly, including rotating the sensor 90 degrees for best use of the pixel-to-frame ratio. I posted pictures of an aluminum bracket to mount the sensor and support the tube. If one were to take the trouble of printing the tube assembly, it would be good to design/include means for supporting it (a provision for a good bracket?).

Hope this helps.

All of your comments help tremendously.
My Prusa MK3S printer is from 2019 and I see them being sold rather cheaply now that the MK4 model is out, and the quality it produces is impressive. Making the “1-32 UN 2A” thread (32 threads per inch (0.794 mm pitch)) is quite possible.
I use the standard / default vertical shells in Prusa slicer (2 lines, unless sloping), and an infill between 15-20%. The thickness of the model’s circular wall is a little over 3mm and very rigid/strong (even with PLA-plastic), and still relatively light.
The nice thing about having a 3D model is that anyone can take the model and change it to their liking, meaning that extra support can “easily” be added to the model if need be, or a new model could be made to allow the tube to rest on, or squeeze around the tube.

BR
Chris