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About red safelights. How much red is damaging for the paper


CamiloRozo

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Hi.

I have a darkroom and I need to shoot a high quality video of the printing process and the safe lights are not strong enough for my purposes. I was wondering how convenient is it to put a large red filter over a medium window (at the moment is covered with black plywood) so I can work with daylight and still prevent the paper from fogging. ¿Somebody recommend doing that? ¿How red (dense) should the filter be? ¿How can I measure that? ¿What's the less sensitive paper to red light that I can use to prevent fogging? I guess is a matter of trial and error but I need some opinions first.

 

Thanks a lot

 

Camilo

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The paper question is easier. A blue-sensitive-only single-grade bromide paper should be less sensitive to red light than a poly/variable-contrast paper, which is sensitive into the green (in order for the vari-contrast magenta and yellow colored contrast filters to work.)

Ilfobrom being one obvious choice, but I'm not sure what else is still made (could be a few options).

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As to filtering a window to get more brightness, the problem is that the total "wattage" or amount of light still makes a difference even with a red filter. Photo paper will fog under even red light (eventually) if the light is bright enough. You will be limited to 7.5-25 total effective wattage, at least 4 feet/1.2 meters from the paper, (and that is "classic tungsten equivalent" wattage, not LED wattage).

And not all "red" filters are the same - some may "look" red, but still leak some light in the yellow-green or UV range, which can fog paper. You will want to be able to get detailed technical specs from whoever makes your filter material as to what wavelengths it blocks and what it allows through, to be sure it's "safe."

Probably something the exact equivalent of a Kodak Dark Red #2 safelight filter is what you'd need - possibly layered with a neutral density (dark gray) filter as well (or a really overcast day) to really reduce the brightness of the window to almost as dark as your regular safelight.

https://www.kodak.com/content/products-brochures/Film/KODAK-A-Guide-to-Darkroom-Illumination-K-4.pdf

There's a simple test for safelight safety. Take out a sheet of your photo paper under the light you plan to use, and lay it in your work area face up with a coin on it for 5 minutes. Develop the paper, and if there is a visible white circle where the coin was, then the paper got fogged, and the light was too bright (red or otherwise). That Kodak document linked to above describes a more complete and complex test.

Of course, for a video you may be able to "cheat" a bit - a minor amount of fogging like this gray >>               probably won't be obvious to the video audence. ;)

You may have to resort to infrared "night-vision" lighting, if your video camera can work with it (some Sonys have a night-vision mode).

 

Edited by adan
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I think you could get away with some red curtains etc. Many years ago as an educational project I made portable tent that was a walk-in darkroom, a lens in one end to make portraits of sitters outside, and a contact printing section at the other end to make resin prints. People could wander in and have a look at how prints were made. The only 'safelight' was the ambient daylight filtering through the red plastic tarpaulin material the tent was made from. It got very hot inside in sunshine, but the tarp material still worked well as a safelight. I think if you choose the paper wisely and follow Andy's recommendation it could work, or at least cost very little to find out.

Edited by 250swb
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We can have much lighter darkrooms than we generally think. I have a darkroom of about 35 square meters (it is also my workspace) and have about 14 simple yellow green bulbs hanging from the ceiling in wall sockets. These bulbs are always more than 2 meters away from the paper and they switch of when I expose. I have tested this several times, never having a problem. Also not when using multigraded paper. I have been filmed in there a couple of times, with digital cameras like the Canon 5d, it was surprising how much came out.

Your idea of red foil against a window is not stupid. I did that in home darkrooms and we had that in a professional darkroom in Paris, early eighties. We used a red foil that came from the printing (as in printing books) world and I believe it was called masking foil. Wonderful to be in contact with the outside world being in the darkroom all day. When the sun was too strong we simply pulled dark curtains over the windows.

You can fake the setting up of the negative . . . and even exposing, burning and dodging. It is when the paper goes into the developer that it becomes interesting to show how the image comes up. But after that you can fake it again.

Edited by M.Hilo
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  • 2 weeks later...

You could fake the developing stage by processing and fixing three or four prints at different stages of development and switch them in  the dish from light to dark  to make it look as if they were one print coming up in the dish. Then you can have more light in the room to film the process.

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On 10/12/2021 at 6:34 AM, adan said:

<snip>

There's a simple test for safelight safety. Take out a sheet of your photo paper under the light you plan to use, and lay it in your work area face up with a coin on it for 5 minutes. Develop the paper, and if there is a visible white circle where the coin was, then the paper got fogged, and the light was too bright (red or otherwise). That Kodak document linked to above describes a more complete and complex test.

Of course, for a video you may be able to "cheat" a bit - a minor amount of fogging like this gray >>               probably won't be obvious to the video audence. ;)

<snip>

 

Yes, pre-fogging the paper is essential as this gets the silver halide past the threshold point of its characteristic curve where it starts to react to light. As Adan said, only a light grey is needed - easily tested by not exposing another part of the paper. In the coin-on-paper safelight test you are looking for differences between the part under the coin and the part exposed to the safelight, not actual density values.

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