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Post by echnaton on Nov 28, 2006 11:55:44 GMT -4
A very good illustration of the issue, Bob
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Post by Data Cable on Nov 28, 2006 12:41:33 GMT -4
While I can't find an alternate scan of AS15-90-12256, cited above, I did find some of a few earlier frames. From Apollo Image Atlas, with white specks in the sky: AS15-90-12244AS15-90-12245And the same frames from the Project Apollo Image Gallery, without specks: AS15-90-12244AS15-90-12245As to what caused it? My first guess, stray dust somewhere along the optical path of the scanner used to digitize these images.
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Post by HeadLikeARock (was postbaguk) on Nov 28, 2006 13:49:59 GMT -4
While I can't find an alternate scan of AS15-90-12256, cited above, I did find some of a few earlier frames. From Apollo Image Atlas, with white specks in the sky: AS15-90-12244AS15-90-12245And the same frames from the Project Apollo Image Gallery, without specks: AS15-90-12244AS15-90-12245As to what caused it? My first guess, stray dust somewhere along the optical path of the scanner used to digitize these images. Here is a scan of AS15-90-12244 on the ALSJ www.hq.nasa.gov/alsj/a15/AS15-90-12256HR.jpgNot only does it not show the same white specks in the sky, but you can even see that the prominent white speck in the lower right foreground on the first scan is not a surface feature as it is not present in the ALSJ scan. Now, that certainly wasn't a star...
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Post by lionking on Nov 28, 2006 15:56:20 GMT -4
so they didn't point up the camera to the sky bcz.. I mean that "Setting the camera exposure to record detail in a sunlit object means that extremely faint objects like stars are outside the range of what the film can record. " wouldn't apply because you would reduce the reflectivity of the surface and yu don't need to take photo of soil, or I still don't understand maybe.
"But as you can see, the exposure was long enough in this case that we can begin to record the images of stars".
So why wasn't there long time exposure to record the stars? and how much time does a long-time exposure take?
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Post by AtomicDog on Nov 28, 2006 16:04:03 GMT -4
Several seconds, and you would have to use a tripod, which they didn't have, or need. Aside from the Apollo 16 UV telescope, they weren't there to take pictures of stars.
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Post by AtomicDog on Nov 28, 2006 16:13:19 GMT -4
so they didn't point up the camera to the sky bcz.. I mean that "Setting the camera exposure to record detail in a sunlit object means that extremely faint objects like stars are outside the range of what the film can record. " wouldn't apply because you would reduce the reflectivity of the surface and yu don't need to take photo of soil, or I still don't understand maybe. I don't understand. You're asking the astronauts to take a picture on the lunar surface, pointing the camera up to remove the lunar surface from the camera's field of view, (because otherwise all you are going to get is an overexposed blob) and make a time exposure to record stars (bear in mind that the Apollo 16 UV camera did exactly this). So without the lunar surface in the photo, how do you prove it was taken on the moon? In other words, what's the point?
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Post by lionking on Nov 28, 2006 16:27:44 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal.
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Post by hplasm on Nov 28, 2006 16:34:34 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. A few billion dollars for a few 'shiny star' pictures is a big deal; What is the point of going to the moon for that?
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Post by Mr Gorsky on Nov 28, 2006 16:35:50 GMT -4
But we can (and frequently have) taken pictures of the stars from Earth.
Given that they are all in exactly the same positions in the sky as they would be if viewed from earth, and the only difference in their appearance is the limited effect of looking at them through an atmosphere, and given that the purpose of the Apollo landings was to study ... well, the moon ... my question would be "What's the point?"
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Post by AtomicDog on Nov 28, 2006 16:41:15 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. Why would you want to go to the moon to make a photo that would be indistinguishable from one that I could take in my back yard? And, as I keep saying, when they had a reason to, they did take pictures of "shiny stars".
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Post by LunarOrbit on Nov 28, 2006 17:21:02 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. They can take BETTER pictures of stars from Earth based observatories. Going to the Moon to take pictures of stars is pointless.
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Post by Data Cable on Nov 28, 2006 17:31:10 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. It is a big deal. For long-term exposures (anything approaching much less exceeding 1 second, and as I recall someone calculated that photographing stars with the film in question would require an exposure on the order of 30 seconds), hand-held cameras are useless. A human holding a camera simply isn't steady enough, the camera will move to some degree during the exposure, smearing the image it is attempting to record. Now, as pointed out several times above, Apollo 16 took along a UV telescope/camera to take pictures of the stars in the UV spectrum (to which the earth's atmosphere is opaque), so they did, in fact, take pictures of stars from the lunar surface... using proper equipment, which an astronaut holding a camera in his hand or attached to his chest does not qualify as.
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Post by grashtel on Nov 28, 2006 17:31:12 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. Except that taking photos of stars is a non-trivial task, I've tried to do so without success. You need a high ISO film (Apollo had low ISO film best suited for taking photos in bright sunlight), a tripod (Apollo didn't have tripods), a wide aperture (the Apollo cameras probably had sufficient tones), and long exposures (the Apollo cameras probably had a manual mode that could be used for it, but it would be fiddly to set in a spacesuit). And once you have gone through that hassle you will get pictures of stars indistinguishable from ones taken on Earth with slightly better equipment or from low orbit making the whole exercise rather pointless. The only way it would be worthwhile to take photos of stars on the Apollo missions would be to take them in a spectrum of light that doesn't penetrate Earth's atmosphere well enough to be usable from the ground. For example the UV pictures that Apollo 16 took and have been mentioned repeatedly here.
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Post by echnaton on Nov 28, 2006 17:40:39 GMT -4
the point is taking photo of shiny stars, taking a few seconds is not a big deal. Have you ever taken pictures of stars with a regular camera? Unless you add some artistic effects to the photo, like a night time landscape, they are pretty boring. Since the landscape was lit by the sun, that option was out. They did take star photos of scientific interest, but those aren’t that pretty.
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Post by echnaton on Nov 28, 2006 17:57:25 GMT -4
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