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Post by JayUtah on Mar 22, 2007 9:07:10 GMT -4
Actually the color 70mm film was not very sensitive by today's standards. The color print film you buy (if you still buy film) is usually 400 speed, or sometimes 200. Many eons ago, you could get 100 routinely. The Ektachrome film taken to the moon was rated at 160, so just slightly slower than the slowest film you can get easily. Surely the coefficient of reflection from the lunar surface matters, but what matters more is the high reflectivity of the lunar module itself. Reflective materials simply don't require as much light on them to show up in a photograph. That's why they tell you to wear light colors at night. The lighting won't be different, but your ability to be visible in it will be. The LM upper stage is covered in aluminum; the lower stage in aluminized Mylar -- both reflective. You can also use exposure settings on the camera to "open up" (as photographers say) a shadow. Here are two photographs taken seconds apart of the same covered bridge. But in the second, I've adjusted the camera to admit more light. Note how the bridge rafters are now more visible.
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Post by BertL on Mar 22, 2007 10:14:26 GMT -4
Is that a hair on the first photograph?
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Post by JayUtah on Mar 22, 2007 10:21:11 GMT -4
No, it's the letter C.
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Post by BertL on Mar 22, 2007 10:35:10 GMT -4
Now this blog has many photos, i'd found answers to most, rest of the stuff he has is crap. Just this one i find a bit puzzling : When you show a photograph shot on earth showing the same effect, the counter argument from the HBs will probably be that it's not valid because of "atmospheric distortion". And for this time they are actually right (partly): because of the atmosphere on earth, a lot of light goes all ways and lights up otherwise completely shadowed surfaces. Obviously because the moon has no atmosphere and earth has, the photographs are incomparable. By giving the "Moon reflects 7% figure", the HBs try to give you the impression the Moon's surface is not reflective enough to light up the backside of the LM. So here's some more brainwashing psychology for you, only from the other side: the moon is so reflective that it can make shadows of objects at night. I know this from experience as I bicycle to school every day (no lights around me, only grass), and one cold winter morning when it was still dark the full moon casted a shadow of me bicycling. It was actually a very surreal and awesome experience. So basically, what I'm trying to say that the 7% reflection of the moon is able to cast shadows on earth. So why wouldn't that 7% be enough to light up the back of an LM that's on the reflective surface itself? (This might be seen as a sloppy argument, but it's not half as sloppy as the HB argument)
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Post by Count Zero on Mar 22, 2007 10:38:00 GMT -4
Another more empirical way to consider the issue works like this (my thanks to those who taught me): As you say, the lunar surface reflects around 7% of the sunlight that falls on it. The polished aluminum* skin of the ascent stage reflects maybe 30 - 40%, and the specular reflection from the mylar on the descent stage might be 60 - 80%. If the LM is lit only by the light reflected from the surface, then the specular highlights on the descent stage will be nearly as bright as the lunar surface, and the ascent stage will be a bit less than half as bright. When we look at AS14-66-9306, that is pretty much what we see. _________________________________________________ *I'm back from my holiday in New Zealand, so I don't have to say "aluminium" any more!
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Post by AstroSmurf on Mar 22, 2007 12:41:26 GMT -4
Careful, Jay. If you keep going like this, we might start thinking you have a sense of humour ;D
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Post by JayUtah on Mar 22, 2007 14:00:33 GMT -4
It would be more dangerous to think i didn't have one.
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Post by nomuse on Mar 22, 2007 14:30:26 GMT -4
Would it be a little more correct to say the gold mylar looks the way it does in this picture not because light is falling on it, but because it is a mirror in position to see some bright ground? It occurred to me right-off that even if the shadow directly behind the LM is deep, the mylar is crinkled and could be showing little scraps of what is to either side of the LM.
Okay, not said very well. Morning coffee is still in the filter.
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Post by sts60 on Mar 22, 2007 14:57:53 GMT -4
I took a look at that site, and what a bunch of warmed-over limp old HB claims it is. Once again, the ability to work a computer is shown to be not correlated with the ability to actually think.
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Post by JayUtah on Mar 22, 2007 15:32:53 GMT -4
Would it be a little more correct to say the gold mylar looks the way it does in this picture not because light is falling on it, but because it is a mirror in position to see some bright ground?
That's very defensible. In fact it relates to an old David Percy claim: the one where he says the United States decal on the side of the LM is improperly lit. He calibrates the overall lighting using the surrounding Mylar, which is mosly reflecting an image of the black sky, and says that there's no way the decal could be lit by enough light under those conditions. He attributes the blackness of the surrounding Mylar to the total lack of light striking it, not the relative lack of light reflecting from it to the camera.
In the general image analysis sense, you always need to be aware of the optical properties of your purported materials. I remember someone trying to tell me about the anomalous shadow falling across a piece of equipment inconsistent with the overall lighting direction. But in fact the equipment had a highly-polished surface and was reflecting object's own shadow falling onto the ground in front of it.
Try to cast a shadow on a mirror. Just try. (Well, okay, a clean mirror.)
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Post by nomuse on Mar 22, 2007 15:47:11 GMT -4
Heck, I think I cribbed it from you in the first place.
But I've certainly seen -- and on occasion been bemused by -- that effect while lighting the stage. Seems like a controlled environment, I know. But some really funny stuff can still happen and you find yourself in the middle of a rehearsal going "how the heck did that spot over there get to be a totally different color than the rest of the stage (and what do I need to do to fix it?)"
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Post by gillianren on Mar 22, 2007 16:35:33 GMT -4
I have to say, I think the first photo of the bridge is prettier.
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Post by JayUtah on Mar 22, 2007 17:46:58 GMT -4
Lighting for Ballet West is a chore. They put down their highly-polished decking, then the scenic artist complains that every instrument you focus throws an ugly caustic reflection onto his scenery.
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Post by Count Zero on Mar 22, 2007 18:45:08 GMT -4
Clavius taught me the difference between specular and diffuse reflection, which is why I specifically identified the type coming off of the descent stage in reply #49.
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Post by SpitfireIX on Mar 22, 2007 19:00:34 GMT -4
No, it's the letter C.
Jay, will you please stop making me laugh out loud when I'm using a computer in the library? That's at least the third time. ;D
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