JayUtah
Penultimate Amazing
It's not as if she can demonstrate a proper understanding of anything else she's posted in this thread. So far we see ignorance of:
- Apollo photography cataloguing and distribution,
- exposure settings required for photographing stars,
- mechanics of orbital rendezvous,
- the difference between minutes and seconds,
- falloff from studio lighting,
- physics of balance and vestibular capacity.
Yes, over a long time old photographs displayed where sunlight can fall on them will fade. This has been common knowledge amongst archivists for as long as I can remember. I would ordinarily say we need a scientific paper to tell us this in the same way we need a chemist to tell us water is wet. But of course the goal there is to quantify the effect and scrutinize the physical and chemical mechanisms. This would inform conservation and restoration exercises.
In the kind of photography the paper descries (black-and-white printmaking), the silver salts react to light and subsequent chemistry by shedding their silver so that it can turn back into metallic silver. It's the metallic silver itself that becomes the pigment you see in the print. What the paper found was that UV light causes the metallic silver to oxidize. Silver oxides and silver sulfides aren't the right color to be pigments. This is what creates the bluish haze on these old pints.
Instead, color reversal photography (color slides) is a dye-coupled process. Silver salts couple with dyes and fix the dyes into the emulsion layer (one for each primary color) proportional to the light-sensitive silver-salt reduction process. During development, the metallic silver, the remaining silver salts, and the unused dyes are washed away, leaving only the dyes that were photochemically coupled and fixed. There's no silver to react with the UV and oxidize.
That said, UV will certainly react also with dyes and cause them to fade and shift hue. Also, the dyes shift for other reasons having nothing to do with UV. If you leave a color slide out in the sun, it will fade and shift. It will also shift sitting in a dark, temperature-controlled room. This is just the nature of dyes.
All of that is still an archivist's discussion. It's what happens over years of exposure in finished photography. Allen is trying to talk about what he thinks would happen relatively instantaneously. Allen claims unfiltered solar UV will "fog" the film. And indeed newbie photographers often ask why their outdoor photographs look hazy and blue. The instructor will tell them it's because of ultraviolet light and recommend a UV filter—cheap and effective.
It's important to know why and how this happens. UV light scatters in air more readily than longer wavelengths. When UV light comes down, the atmosphere preferentially redirects it (scatters it) in all directions, including horizontally outward and into your camera lens. It does this with visible blue light too, which is why the sky is blue as seen from Earth. You can't see the UV wavelength, but your film can. Without some correction, the film will respond to UV light preferentially in the blue-sensitive emulsion layer. You lose contrast (i.e., the photo is hazy) because the scatter is coming into the lens from all directions, so it affects the entire field of view even in spots where the desired image isn't especially blue.
Film manufacturers correct for a certain expected amount of UV by adding a UV filtration layer on top of the emulsion. Those of us who photograph at higher altitudes where there is less atmospheric UV attenuation need filters because the UV-blocking layer isn't enough. There's a sour spot up in the mountains where there remains enough air to scatter the UV but less air to absorb it an remove it from the photography equation.
Now the punchline.
This only happens when you have an atmosphere. You don't have one of those on the Moon. To be sure, objects that you photograph will be reflecting and scattering more UV than usual, because you have absolutely no UV attenuation in the lunar environment. But that's easily corrected, and doesn't affect the whole field of view. Remember the UV-blocking layer on the actual film I mentioned above? You just spray that layer on a little thicker. Problem solved. But it is hilarious that Allen knows so little about photography that he doesn't actually know why UV-uncorrected photos appear foggy and why that wouldn't happen on the Moon.
