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Earth Photography from the ISS
While reading the BBC website (see following link) I noticed a
fascinating detail: They suggested that it was difficult to photograph the Earth using telephoto lenses on the ISS due to the movement of the platform. Having tried to follow the ISS with a telescope I can sense the problem in reverse. Given the interest in Earth surveillance from space this seemed like the basis for an interesting discussion. Is the problem one of low orbit and high relative speed of the ISS in comparison with other photographic/surveillance platforms? Or the small aperture and low relative shutter speed of hand held cameras? One would imagine the security services "Hubble-type" platforms have a very long focal length and very high magnification to achieve their objectives. These " Inverted Hubbles" must have some orbital velocity or they would simply fall to earth. Perhaps parallax effects and relative velocities can be overcome with very high speed (cost no object) imaging sensors? Is the Earth really such a low light target for orbital hand held cameras? Or is the problem simply one of the very large distances involved (from orbit) requires long and "slow" lenses to show any detail on the ground with hand held cameras? http://news.bbc.co.uk/2/hi/science/nature/7668965.stm |
#2
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Earth Photography from the ISS
"Chris.B" wrote:
Or the small aperture and low relative shutter speed of hand held cameras? I think you've nailed it right there. One would imagine the security services "Hubble-type" platforms have a very long focal length and very high magnification to achieve their objectives. These " Inverted Hubbles" must have some orbital velocity or they would simply fall to earth. Perhaps parallax effects and relative velocities can be overcome with very high speed (cost no object) imaging sensors? Could well be, but I would think a "push-broom" camera (time-delay integration), as used on Mars orbiters, would be a better bet. |
#3
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Earth Photography from the ISS
Chris.B:
While reading the BBC website (see following link) I noticed a fascinating detail: They suggested that it was difficult to photograph the Earth using telephoto lenses on the ISS due to the movement of the platform. Having tried to follow the ISS with a telescope I can sense the problem in reverse. Given the interest in Earth surveillance from space this seemed like the basis for an interesting discussion. Is the problem one of low orbit and high relative speed of the ISS in comparison with other photographic/surveillance platforms? Or the small aperture and low relative shutter speed of hand held cameras? One would imagine the security services "Hubble-type" platforms have a very long focal length and very high magnification to achieve their objectives. These " Inverted Hubbles" must have some orbital velocity or they would simply fall to earth. Perhaps parallax effects and relative velocities can be overcome with very high speed (cost no object) imaging sensors? Is the Earth really such a low light target for orbital hand held cameras? Or is the problem simply one of the very large distances involved (from orbit) requires long and "slow" lenses to show any detail on the ground with hand held cameras? http://news.bbc.co.uk/2/hi/science/nature/7668965.stm I'm skeptical. I probably can't work out the geometry, but it's not like being in a low-flying aircraft at, say, Mach 1 and watching the scenery go by below you; the apparent speed at which the Earth passes under you from low-Earth orbit is less than that from a fast, low-flying jet. Actually, anyone who has flown over a land mass in a commercial airliner on a clear day has observed this. It's easy to take a sharp photo of the ground from 30,000 feet @ 500 mph, but not so easy from 300 feet at 200 mph. There are many good photos taken of Earth from the shuttle with ordinary equipment. It's a bright object that lends itself to short exposure times. The more detail you want on the ground, the more focal length you will need, and the slower the lens will be. I would think that a 300 mm Ÿ2.8 lens of the type favored by sports photographers might do a decent job. If you need resolution on the order of a few millimeters then you are going to have to try to get hold of a photo reconnaissance satellite. Davoud -- Don't re-elect the failures of the past eight years. usenet *at* davidillig dawt com |
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Earth Photography from the ISS
On Fri, 17 Oct 2008 18:30:38 GMT, Davoud wrote:
I would think that a 300 mm Ÿ2.8 lens of the type favored by sports photographers might do a decent job. If you need resolution on the order of a few millimeters then you are going to have to try to get hold of a photo reconnaissance satellite. I think a few millimeters is out of bounds for anything up there. But you can do a back-of-the-envelope calculation for the sort of equipment somebody is likely to take on the ISS. A 500mm lens with a typical digital camera has a resolution of about 2.5 meters per pixel at the height of the ISS. I doubt the lens will actually be good enough to deliver that, but we'll take it anyway. For a nominal orbital (ground) speed of 450 km/h, or 120 m/s, that means you'll have one pixel of blur in 1/50 second. So if you're trying to achieve maximum resolution, especially if you're using a small telescope (with at least several inches of aperture and 500mm or more of focal length) it does seem likely that active tracking would be required _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#5
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Earth Photography from the ISS
In article , Davoud wrote:
I'm skeptical. I probably can't work out the geometry, but it's not like being in a low-flying aircraft at, say, Mach 1 and watching the scenery go by below you; the apparent speed at which the Earth passes under you from low-Earth orbit is less than that from a fast, low-flying jet. Actually, anyone who has flown over a land mass in a commercial airliner on a clear day has observed this. It's easy to take a sharp photo of the ground from 30,000 feet @ 500 mph, but not so easy from 300 feet at 200 mph. There are many good photos taken of Earth from the shuttle with ordinary equipment. It's a bright object that lends itself to short exposure times. The more detail you want on the ground, the more focal length you will need, and the slower the lens will be. There are some quite exotic lenses available on the Space Station, including a 400/2.8 with teleconverter (http://www.kenrockwell.com/nikon/ima...8/MVC-157E.jpg for a known-to-be-a-Nikon-400/2.8 and http://spaceflight.nasa.gov/gallery/...s007e13547.jpg for the camera in use on the Station, with the rest of their fairly impressive photographic kit velcroed to the wall) http://spaceflight.nasa.gov/station/..._letter10.html writes about photography from ISS. The interesting article (http://www.airspacemag.com/space-exp...auts_View.html) I read was about taking photos of cities *at night*, where you want a reasonably long exposure, and they concocted a barn-door mount out of bits and pieces lying around on the Space Station with which they got some really spectacular shots. Tom |
#6
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Earth Photography from the ISS
starting last week a radioamateur Richard Garret is on ISS board and
he is transmiting images in SSTV mode Robot36 for all radioamateurs in the world on 145.800 mhz also voice FM comunications. Info details at www.issfanclub.com and www.amsat.org |
#7
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Earth Photography from the ISS
On 18 okt, 00:02, yo9gjx wrote:
starting last week a radioamateur Richard Garret is on ISS board and he is transmiting images in SSTV mode Robot36 for all radioamateurs in the world on 145.800 mhz also voice FM comunications. Info details atwww.issfanclub.comandwww.amsat.org It is Garriot. Never played Ultima? http://en.wikipedia.org/wiki/Richard_Garriott |
#8
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Earth Photography from the ISS
Thanks for your thoughts and to Thomas Womach in particular for those
excellent links. The barn door mounting driven by a drill was very clever and displays the skills of those involved. Rather more sophisticated than my rubber wheel and cone variable speed drives. It's odd how cluttered the modules appear in interior shots. I can just imagine them saying: "You're not coming down again until you tidy your room!" ;-) |
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