Little Gray Riding Hood?

February 8, 2008 8:14 PM

Ok, here's a slightly odd one. Prompted by the recent FPP in the blue about the ancient photography lab, I got to thinking about the lighting in the basement "wet lab". This led to the question: if film doesn't react to red light, why are we able to take pictures of red things?
posted by Malor to media & arts (17 comments total)

Short answer: black and white film can NOT be opened in red light. Developing must be done in total darkness. B&W paper is "blind" to red light, seeing it as black.
posted by The Deej at 8:19 PM on February 8, 2008

Black and white film doesn't react to red light. Color film does. If you take a picture of something red using black and white film, it comes up as black. Look at the black and white versions of this apple.

(Note: Not a photographer.)
posted by kingjoeshmoe at 8:20 PM on February 8, 2008

Nevermind. The Deej no doubt knows way more than I do.
posted by kingjoeshmoe at 8:21 PM on February 8, 2008

Color photographs are developed in total darkness, because that paper is reactive to red light.
posted by mhp at 8:21 PM on February 8, 2008

Modern panchromatic BW film does react to red light and has to be developed in total darkness. Old fashioned orthochromatic film was more blue sensitive than red-sensitive, and could be briefly inspected in red light. The results looked like they had been shot through a blue filter, resulting in dark or swarthy complexions which you will recognize instantly in old photos once you are used to seeing them.

Old films were also generally slower which gave more latitude in using a red safelight.

All colour film is panchromatic and has to be developed in darkness.

Black and white paper is mostly orthochromatic (although multigrade paper is only semi-orthochromatic) which is why you can use a red safelight to make prints in a darkroom.

I have a darkroom downstairs and I never use a safelight (red/brown) for developing film although even with panchromatic BW film it is theoretically possible to use a dim green light to inspect pan film as it develops.

Most representations of darkrooms on film/TV are ludicrously wrong.
posted by unSane at 8:22 PM on February 8, 2008 [1 favorite has favorites]

Safe-lights are very specific to the film. What looks red to your eyes outside the lab is reflecting more of the light spectrum than your safe-light is emitting. Try lighting that red object (or anything else) using a safe-light, and you won't see anything, either.

Just because something seems red doesn't mean it's not reflecting some violet and some oranges and some yellow, all which affect (most) film.
posted by cmiller at 8:22 PM on February 8, 2008

BTW Kingjoeschmoe is completely and utterly wrong.
posted by unSane at 8:23 PM on February 8, 2008

I just want to reiterate that if you look at the frequency response of modern panchromatic BW film (which is pretty much ALL BW film -- ortho film is really hard to get hold of -- it has plenty of sensitivity in the red range). So all these answers which imply that red objects don't register are just wrong. Try developing a BW film under a red safelight and see what happens.

Or, if you have anything on the roll you care about, don't.

Also, try photographing a Pantone or Kodak colour chart. The pure red squares will NOT be pure black if you use panchromatic film (eg Tri-X, HP5, FP4, Pan-F, Ilford Delta, Kodak T-max and pretty much EVERYTHING else that isn't a technical or an ortho film).
posted by unSane at 9:16 PM on February 8, 2008

Hmm, I was nearly certain I'd seen real darkrooms with red lights. Am I misremembering?
posted by Malor at 9:27 PM on February 8, 2008

Malor, not at all. Red safelights are still used for making prints (although multigrade papers are somewhat red-sensitive). You just don't use them when handling film.
posted by unSane at 9:35 PM on February 8, 2008

No, Malor, you aren't misremembering. The distinction that others have made above is that black and white film should be developed in darkness, while black and white paper can be developed with a red light. The difference is in the relative sensitivity to red light (film is more evenly sensitive, while paper is less sensitive to red light) and in the overall sensitivity (film is much more sensitive than paper).
posted by ssg at 9:36 PM on February 8, 2008

red lights are for B&W "paper" only, not film. film records red, but the paper need only see black or white, light on, or light off, and of course the in between shades, but the color does not matter, so to make things easier in the darkroom, the paper is not red light sensitive allowing you to have some light source while you use it.
posted by caddis at 10:02 PM on February 8, 2008

Film turns into negatives when developed.
Negatives projected onto paper = prints.

In case anyone was still confused on the distinction between B&W film and B&W paper.

When I learned darkroom, we had a light-safe closet where we loaded the film into the tanks to develop it. This was separate from the actual dark room.
posted by smackfu at 10:13 PM on February 8, 2008

Note that even red light isn't necessarily "safe" for unfixed printing paper in the long term; if you leave it sitting out in a darkroom with the lights on in the long term, you'll end up gently exposing it, leading to an overall greyish cast instead of bright whites in the developed and fixed print. But that's not practically speaking a problem; printing paper is usually kept secured in a light-proofed container of some sort when it's not being used.
posted by cortex at 7:30 AM on February 9, 2008

This brings back memories of developing color prints in college. We had three light-safe rooms around a common room which held the color print developing machine. You'd go in your little room, load your negative, get it all focussed and then turn off the light and, by touch, get your paper out of the box and place it to receive the image. Then, in total darkness, go to the common area and put it in the machine. Often there would be someone else standing in the common area waiting for their print. You'd chat -- sometimes it would be a classmate, sometimes someone from another class. Sometimes you'd never see them! It was strangely intimate and foreign. Then you'd grab your print, isolate yourself in your little room, turn on the light and see what you got!
posted by amanda at 8:14 AM on February 9, 2008

Thanks for all the good answers... feel free to keep commenting if something else comes up, I'll keep checking back. But I'm satisfied my question was answered: I misunderstood what a red light did in photography. :)
posted by Malor at 2:41 PM on February 9, 2008

I misunderstood what a red light did in photography. :)

Understandable, since tv or movies only show developing of prints, and can't realistically portray loading of film onto the developing reel, since that takes place in total darkness.

However, once the film is loaded onto the reel, it is put into the tank. The tank can then be taken into regular light, since the lid allows you to pour the appropriate chemicals and water in and out without the light getting to the film. Once the agitation and rinsing is complete, the finished negative can of course be inspected in normal light.
posted by The Deej at 3:51 PM on February 9, 2008