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116 points williamsmj | 1 comments | | HN request time: 0s | source
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flimsypremise ◴[] No.42311078[source]
As someone who has built multiple custom macro film scanner setups, owns basically very consumer film scanner of note (including the Coolscan 9000 and the Minolta Scan Multi Pro), and is intimately familiar with the workings of various film scanners and science of digitizing film, I don't think this article provides particularly good advice.

Just for instance, the LS-2000 features in the post has an advertised optical resolution of 2700DPI, which means the absolute maximum megapixel resolution you can get out of that thing is a little over 10MP. Film scanners are notorious for overstating their optical resolution, which has nothing to do with the resolution of sensor used to digitize the image data and everything to do with the lens in the scanner. You can have a 200MP sensor scanning your film but if your lens can only resolve 1000DPI you will have a very high resolution image of a low resolution lens projection. It's maybe a little better than a flatbed and it features dust removal, but in the year of our lord 2024 the LS-2000 is not a good choice for scanning film.

As for his macro scanning setup, he appears to be using the digitaliza for film holding, which is a notoriously bad product with many known flaws. Negative supply makes a line of lower cost version of their very good film holders, and Valoi also offers an affordable system of components that I highly recommend. There is a ton of good information out there about macro scanning, and had the OP sought it out he could avoided his little adventure in retro computing.

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enthdegree ◴[] No.42311993[source]
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.

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sdflhasjd ◴[] No.42312213[source]
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.

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flimsypremise ◴[] No.42313064[source]
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.

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1. turnsout ◴[] No.42314288[source]
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?