Seeking advice for 8mm scanner design

Machine Design
1

Hello all,

First post here, but I’ve been a long-time lurker (I think I first heard about Kinograph around 2019). Apologies in advance for the long post!

I’ve got a large collection of standard 8mm and super 8mm films. Some from family and friends, and others from buying job lots on ebay. (I also have quite a lot of 16mm and 35mm film, but that’s outside the scope of this post!). In the past I’ve gotten a few digitized by a local transfer company, and while the results were excellent (I was able to get the individual JPEGs from their frame-by-frame process on a hard drive and do the MP4 conversion myself), the cost is too high to work at scale.

I’m now looking to build a DIY film scanner. I’ve got a decent background in software, have used Arduino and Raspberry Pi before, and have access to a community makerspace with 3D printers, laser cutters, CNC machines, etc. However my knowledge of optics and lighting is basically non-existent.

Below I’ve highlighted the key features that I consider important in a film scanner, along with ones that I am not concerned about. This prioritisation is dependent upon my needs, and I’m hoping that it will make the design decisions easier. I still have quite a few open questions that I am looking for advice on! (Listed at the end).

Things I consider important:

  1. Image quality. My aim is to have “very good” image quality. By this, I mean significantly better than the Wolverine-style scanners or filming a running projector. But I’m not seeking absolute perfection. My goal is to take individual R/G/B frames, each at multiple exposures, at 4K or higher resolution. I’m not seeking “perfection”, especially given that many of these films were taken on inexpensive cameras. For that reason things like a wet gate are beyond the scope of my plans.

  2. Gentle on film. I really, really don’t want the film scanner to damage the films. For that reason I don’t want to modify an existing 8mm projector because I am concerned that the claw that is typically used can damage the film. I would also like the film scanner to work with warped or damaged film (e.g. damaged sprocket holes), although I know there’s a limit here.

  3. Standard 8 and Super 8 compatibility. I have a lot of both types of film and the film scanner needs to be adaptable between both formats. “Adaptable” can mean swapping components (e.g. different rollers / sprockets / gate is needed for each format) but swapping from one format to another shouldn’t take more than an hour or so.

  4. Reel sizes. The film scanner ideally needs to be able to handle reels up to 800ft in size. Most of the films I have are 50ft, but I have some 400ft and a few 800ft reels. If absolutely necessary, I would be willing to limit the reel size to 200ft, but this would then require me to cut and splice the larger reels, which I really want to avoid if possible.

Things that I do not consider to be important:

  1. Speed. The scanning process does not need to be fast. If it takes multiple hours to scan a 50ft reel, I am OK with that. For this reason I am currently erring towards a stop-and-start scanner, where it positions each frame under the camera before stopping, taking the required pictures, then moves to the next frame.

  2. Sound. I’m planning to build a separate, dedicate machine to handle Super 8 films with sound. The film transport will likely be based on the main film scanner, but with continuous motion and a heavy flywheel to ensure a constant linear speed.

  3. Size. The film scanner itself can be reasonably large. I’m not trying to make something the size of a Wolverine-style scanner! It can be large enough to accommodate a decent lighting setup, a good quality camera, etc.

Open questions:

  1. What sort of gate should I use? I’m wanting to get full-frame capture, but also support damaged and warped film. If there is a 3D-printable design I can adapt, this would be very helpful.

  2. Film transport. There are a few approaches, from using PTR rollers to using the sprockets on the film to avoiding touching the film altogether and feeding from the reels. I’m not sure about the best approach.

  3. Lenses, focusing and lighting. These are topics I know very little about. I’m happy to go with a manual focus setup if I can set it and leave it for hours / days.

  4. Tension. I’m not sure how important tensioning is. And if it is important, how can a film scanner measure it, and from those measurements regulate it?

  5. Infrared cleaning. I’ve heard conflicting things about whether this works on 8mm films (particularly Kodachrome films). As I’m not going with a wet gate, it’s something I would be keen to have if it was viable.

Thanks,
Andrew

2

Welcome to the forum @betamax. I believe your posting was stuck on one of the forum transitions, and only recently posted. I’ll be glad to provide some feedback later, but in the meantime my reply will bring it back to current postings for everyone to see.

3

Ah, thanks for the ping, @PM490 . To be honest, I’d entirely forgotten about the post I made! All my 8mm films are still sitting in storage, waiting for me to do something with them, so it would be good to get feedback on the best way to do this.

Since writing the above post, very little has changed except that I discovered the T-Scann Project, and I think that looks quite close to what I was looking for. I’ll need to do a search of the kinograph forum archives to see what people’s thoughts are on that, and whether it will meet my requirements.

4

With a little bit more time, a quick rundown with some comments and pointers.

Suggest you consider the Raspberry Pico instead of Arduino. Many advantages, one disadvantage is: it does not have NV memory. But settings can be stored at the RPi or PC driving the transport controller (PICO).

Normally when talking about separate RGB the typical setup is a monochrome sensor with R G B illuminant. The pixels (size of the sensor) determine the resolution.
I have been experimenting with separate RGB exposure, using a somewhat novel approach. White LED illuminant and a color (bayer) sensor (the HQ for now). Capturing RAW (each channel with a different light intensity) and binning (combining the Bayer filtered pixels into a 1/2 resolution RGB picture). This approach requires being able to adjust the intensity or the exposure if one wishes different levels for different color channel.

Not sure how well the warped film will work. This is a similar goal of what I have been building, and for that reason I presently have no gate. The sprocket and edge detection is done from the images captured.

Not an issue. I am attempting to also do 16 on the same.

The issue to consider with very large reels and steppers is that the step resolution is lessen as the reel radius increases (perimeter is angle (radiants) x radius). I settled for 400ft with steppers driving the pickup and take up directly. 800ft is certainly possible, but it may require other approaches. It would not be an issue for a design with a gate+pinch roller, like the Tscann.

Budget vs Speed. The faster, the more expensive.

It depends. For claw systems, and pinched roller (like the Tscann) is not as critical. For something like what I am doing with an open gate, it is.

There are multiple approaches at controlling tension, some very simple and loose -like the Tscann on-off switch- others very accurate, like nick’s ReelSlow8 load cell, and some commonly used like the potentiometer arm or dancing hat (which I use).

For the optics, first decide what sensor you wish to use. Many here are using enlarger lenses, many using the Schneider Componon-S 2.8/50mm. Another similar alternative is the Nikor EL 2.8/50mm. For 8mm and the HQ sensor, the lens to sensor distance is around 75mm (depending on crop tightness or full frame) and that will be approximately 90mm from the lens to the film for focus.

On the subject of light, first decide if you are going with a monochrome or color sensor.
For diffused even illumination many have been using an integrating sphere, and for 8mm only is not that big. In my case (8 and 16 mm) I am using a sphere with 100mm diameter. If using white light, look for very high CRI (98+).

In addition to the above, there are great tools shared in the forum. Manuel Angel has made a nice software for the raspberry pi.

Having access to 3D printing and laser cutting (as you mentioned) Tscann is quite feasible and has completed an impressive number of builds.

One area for improving the Tscann is addressing the extensive contact between active film area and the 3D printed components (rollers are flat). I would prefer a roller design minimizing contact to the edges of the film, and if unavoidable, make the contact on the opposite side of the emulsion with silicone or similar surface.

My present design is being tweaked, especially the transport control firmware. Hope to get it good enough to make all components available as open source (laser-cut templates, STLs for 3D parts, and PCBs)

There is extensive know how in the forum you can search for, and many long-time participants will give you great feedback, especially if the posting provides good context and specifics… like you have.

3 Likes