[enthdegree]

Digitizing film seems to be a perennial pain point. As far as I know there is no mostly-automated option to scan multiple film formats at high resolution besides paying someone with very expensive equipment to do it for you. The obsolete equipment like those models you mentioned involves a lot of fastidious labor per-frame and is generally pretty awful.

Modern equipment has similar warts. Flatbed scanners are bad film imagers for a number of reasons, a few which you already wrote. There's a huge volume of new products coming out for scanning right now (film holders, copy stands, light panels, etc) but these setups are very inconvenient to set up or, to be charitable, demand practice and perfect technique. There's always people ready to insist they have an easy convenient time setting up their SLR scanners and capturing 1000 rolls at 9999 DPI in 2 minutes. I don't share their experience.

During the pandemic I tried to proof-of-concept a path forward without any real success:

- The first attempt involved modifying a Plustek scanner to take medium format. This ended up taking a ton of work for each medium format frame (4 captures for each of the 4 quadrants, and each of those is already slow for a single 35mm frame). Stitching these captures is tedious and flaky for images that don't have obvious sharp features.

- The other involved rigging the objective of a Minolta Dimage Scan Elite II on a Raspberry Pi HQ camera onto an Ender printhead to raster over the film with a light table. This could have worked but it had many mechanical problems I am not cut out to solve (lens mount, camera-to-film-plane alignment)

Leaving aside designing a proper optical path there are 2 killer problems:

- the problem of mechanically manipulating the negative and keeping it in focus

- the problem of stitching together partial captures with minimal human intervention

A few people seem to be working on open source backlit line-scanners but as far as I know no central path forward has emerged. I hope someone figures it out.

[sdflhasjd]

I see you mentioned using a 3D printer for scanning medium format film. I did something similar, but took the opposite approach. I placed the film on a lightbox and mounted that to the printer, then had that move around in front of a camera with macro lens. I did not have much of a problem with alignment.

That being said, this was a one-off, but once I had enough overlap with each capture, PTGui was able to switch it together relatively hands-free, even with it having lots of sky.

[flimsypremise]

I've been doing something similar. I started with a 3D printer approach, then two cheap aliexpress C-beam linear actuators and finally managed to acquire a 2-axis microscope stage for cheap. The key I have found is that any issues with alignment can actually be solved with focus-stitching.

The real problem with most scanning setups is actually getting accurate color out of color negatives. The common wisdom these days is to use high-CRI light, but I believe that approach is flawed. Film scanning is not an imaging challenge, but a rather a densitometric one. You don't actually want to take a photo of the negative in a broad spectrum because the dyes in photo negatives were never intended to be used in a broad-spectrum context. You actually need to sample the density of the dye layers at very specific wavelengths determined by a densitometric standard (status M) that was designed specifically for color negative film. Doing this with a standard digital camera with a bayer sensor is... non trivial and requires characterizing the sensor response in a variety of ways.

Basically the hardware is easy, the software is hard.

[turnsout]

Wow, do you have a write up of your scanning setup? It sounds like it could work for scanning 4x5 and 8x10.

I’m also curious about your comments on the light source. Although you’re 100% correct about the way the wavelengths are specified in the data sheets, the reality has always been different. When I was printing color in the darkroom, our enlargers were very basic lights with subtractive color filters. Dedicated film scanners used either fluorescent or basic LED backlights. Have you run into color reproduction trouble that you’re sure relates to the illuminant or sensor response curves?

[jazzyjackson]

Ooo I never thought about the issue of stitching blank space together. I wonder if film grain makes it trivial for the alignment algo.

[enthdegree]

Very interesting. What camera/lens/lightbox did you use and around what DPI you achieve?

[sdflhasjd]

I used an A7C2 + Sony FE 50mm f2.8 macro. The lightbox was a custom build based on the design that I found linked on HN recently: https://jackw01.github.io/scanlight/. This was then mounted vertically on the toolhead of my 3D printer with the camera on a tripod, I then used the Z and X axes to scan across the negative.

Although I had success with PTGui and it "just worked", I didn't fancy paying for it and instead used Hugin in the end. This lead me to take around 63 pictures with 50% overlap.

The film was a 4x5 negative and after stitching I'd say the effective DPI was ~4500