[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?