Light source that compensates for orange mask in negative film?

September 20, 2007 8:27 PM

Let's say I'm toying with the idea of making my own scanner for negative film. I've found a suitable sensor, and the rest of the mechanism looks manageable. Can I get a suitable light source that will compensate for the orange mask, at a reasonable price?

Basically, I'd like suggestions for a good, stable, even light source of a color that will compensate for the orange mask in negative film. I could just do this by trial and failure, but I'm sure there are some standard light sources for this somewhere, perhaps something used to optically duplicate negative film? I'm basically going to put a high-res CCD camera on the other side of the film, focusing through something like a Printing Nikkor, so what I need is a light source that'll light one frame of 35mm film evenly, with a color that will get rid of as much of the orange mask as possible (I guess I can do some detailed calibration in software afterwards).

posted by Joakim Ziegler to technology (17 comments total)

I don't see why you'd need to bother. Wouldn't that be better adjusted digitally post-scan?

You're going to have to do post-scan color compensation regardless, because no matter what light source you use, it's going to be offwhite.
posted by Steven C. Den Beste at 8:53 PM on September 20, 2007

I mostly want to do this because the camera I'm using has 14 bits color depth, and if I need to mess around with the color balance a lot in postprocessing, I'm going to be losing color fidelity per channel. I'm prepared to do some postprocessing, of course, but I'd ideally like the image that comes in to be as balanced as possible, to get as high quality as possible out of the camera CCD.
posted by Joakim Ziegler at 9:04 PM on September 20, 2007

You probably don't want to correct for the orange mask optically, since you want to be able to scan reversal and b&w film as well. (Or do you?)

FWIW, I know the Fuji Frontier uses an array of LEDs and a light box (mirrored on the inside, diffuser on the side closest the film) to accomplish this. I'm not sure what the color tolerances are on LEDs, though.
posted by neckro23 at 9:06 PM on September 20, 2007

There are some adjustable-color LED lighting projects you might consider.
posted by Myself at 9:10 PM on September 20, 2007

Yes, I'd like to be able to also scan reversal and B&W, but negative is much more important, and I would be willing to swap the entire light source to scan non-negative stuff.

But yeah, I've wondered about an RGB LED array, I'm just wondering what it'll take to diffuse and integrate the light enough that it's even, and then get it to be even (as much as possible) over a whole 35mm frame. That's why I figured that a pre-made solution might be preferable.
posted by Joakim Ziegler at 9:17 PM on September 20, 2007

The color head (light source) from a photographic darkroom enlarger would work fine. It will have even tungsten illumination, infrared cutoff, adjustable color and most have stabilized power supplies.

That orange base color is quite complex, don't expect a simple linear solution for color correction.

Also, there are some quite good dedicated 35mm film scanners available for not much money.
posted by Fins at 9:32 PM on September 20, 2007

Fins: How much would that cost? It sounds interesting. I'm not interested in a perfect solution for the orange base color, really, just something that'll give me something decent that I can postprocess afterwards. I'm planning on running calibration film through the thing anyway, so I should be able to get some decent lookup tables out of it.

And yeah, I know about stuff like the Nikon Coolscan, which is very nice. But I want to scan motion picture film, which is a totally different proposition, and the scanners that do that are very overpriced. At least that's what I think, I'm going through the engineering issues now to see if it's worth trying to build something.
posted by Joakim Ziegler at 9:40 PM on September 20, 2007

Omega, Beseler and Durst brands of color heads are/were commonly used for this type application.

I'd look on eBay, Craig's List, camera stores and classified ads, expect to pay $50-250 used depending on a whole lot of factors.

Oh, motion picture film. Never flat, always scratched, a bitch to scan. It really requires specialzed equipment to do right.
posted by Fins at 10:08 PM on September 20, 2007

Fins: I can get a decent gate for motion picture film for a couple of thousand dollars, for instance from Oxberry. That'll be pin registered and with a pressure plate, which should be enough to keep it flat and correctly registered. That might sound like a lot of money, but a motion picture film scanner costs a few hundred thousand dollars, which is why I'm curious if I can't get decent results out of something more DIY, I'm thinking maybe 10k-20k dollars in total.

The color heads seem interesting, when you say "this type application", what are you thinking about specifically?
posted by Joakim Ziegler at 10:15 PM on September 20, 2007

Some of the early digital telecines were built just this way with a Super Chromega head in front of a cine transport. Also 35mm slide duplicators and animation cameras use/used the same configuration.
posted by Fins at 10:29 PM on September 20, 2007

That's definitely very interesting. Will I be able to mess with the color enough on these heads to compensate to a large degree for the orange mask (with the usual disclaimer of its non-linearity, etc.)? I'm assuming yes, since you can use them to produce very strong casts when printing from negatives...
posted by Joakim Ziegler at 10:38 PM on September 20, 2007

Yes, individual control of cyan, magenta and yellow with a range over 170 CC.

Looks like they are still available new.

However, I think light is the least of your worries, you must have a liquid gate and dead perfect optical alignment.
posted by Fins at 10:59 PM on September 20, 2007

No one really uses a liquid gate for motion picture film scanning, outside of the people doing restoration work (Oxberry sells a system for some 15-20k dollars, though). Normal film scanners like the FilmLight NorthLight use a standard pin registered gate.

The alignment is important, that's true, I'm thinking about using an optical table with some optical translation stages to align everything. They're not that cheap, but you get pretty far with a few thousand dollars.

As I said, that's still within the budget range that makes the project interesting, since the NorthLight, for instance, costs about 350k dollars. The cheapest scanner available that I've seen is the Lasergraphics Director, which is 200k dollars, and seems to only do 2k native resolution.

Anyway, you've been very helpful with my question, I think I'll flag this as answered now.
posted by Joakim Ziegler at 11:37 PM on September 20, 2007

It has been about 10 years since I have tried to scan negatives, but from what I remember, each manufacturer / brand / speed / etc.. has a slightly different colour as a base. Even the same film over time will be a little different hue. When I scanned a negative in, I had to scan a bit of the unexposed frame to get the base color, get an average color value for that film, and add an opaque layer with the inverted value of that color as a starting point. It worked pretty well.

I think this is the easiest manual method, but it may be possible for you to determine they base colour of your negative, invert it, print the inverted color it on clear film, and use this printed film to shade your light source. Then if you have a different base colour, you just print a new film.

Let us know if you find a nice solution.
posted by Yorrick at 11:55 PM on September 20, 2007

I guess I should have previewed a little better to catch the typos in my second paragraph but it is very late.
posted by Yorrick at 12:03 AM on September 21, 2007

Another thought: Use the same method to find the inverted color of the mask, then display this colour on a flat CRT or LCD screen and use this as your light source. Diffuse with a mylar sheet if needed.
posted by Yorrick at 12:19 AM on September 21, 2007

Why not buy an old high quality scanner to use for parts? You can get one on Ebay for $30-50 and cannibalize it for parts. I have an old Polaroid Sprintscan that uses a cold light source of which I have a few extras but using an old one for parts is probably your best resource.
posted by JJ86 at 5:59 AM on September 21, 2007