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Re: AO-40 Pictures



At 11:26 PM 12/1/2000 -0600, Jon Ogden wrote:
>Yeah, I think it's on the edge of the satellite.  I think it's on the same
>side as all the high gain antennas, etc.  So as the bird spins, it will
>move.  It matters not that the direction is parallel to the spin axis, it
>will still move about it and hence distort the picture!

Well, that's not right. It's the direction the camera points that matters,
not its position on the spacecraft.

If the camera points along the spin axis, then the image ROTATES
during the exposure. The camera also shakes a little, but excursions
of a couple of meters aren't going to change a picture of an object
that's at least 600 km away, as long as the camera stays pointed in
the same direction. It's as if you aimed your hand-held camera at
the moon and took a picture in landscape mode, then walked a mile,
aimed the camera at the moon again, and took another picture in
portrait mode. Except for the rotation, the two pictures would be
almost identical. Walking a mile had almost no effect.

If, on the other hand, the camera points perpendicular to the spin
axis, then the image TRANSLATES during the exposure. That's
different. If the camera is mounted with one side parallel to the
spin plane, then the translation would show up as compression
of the image in that direction.

My little low-precision experiment with Photoshop seemed to be
consistent with compression of the image in a single axis.
I certainly didn't do enough checking to rule out rotation, though.

73  -Paul
kb5mu@amsat.org

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