ASTRO STEREO

[Paul S. Boyer <boyer@xxxxxxxxxxxxx>]

ASTRO STEREO
Lyle Murphy writes that he would like to make stereo photos of the
stars using a 100-mm reflecting telescope and the rotation of the
earth to obtain enlarged stereo base.
I do not think that this would be successful, because the maximum
base you could obtain from the Earth's rotation would be twice the
radius of the Earth, or about 12740 km, shooting at sundown and
sunrise (and you'd actually have less time than that), and you'd have
a smaller potential base if you were at a higher latitude than the
equator.
Stereo infinity is about 10000 times the base, or 127,400,000 km in
this case, which is not even the distance to the sun (about
150,000,000 km).
If you used the Earth's revolution about the sun to get a bigger
base, taking pictures six months apart, you would have a potential
base of 300,000,000 km.  That would enable you to get a stereo effect
up to 3,000,000,000,000 km away.  Are there any other stars that
close?  If you own a 'scope, perhaps you know.  But the stereo effect
would be very unimpressive at these distances, so close to "stereo
infinity."
For over 100 years folks have taken stereographs of the moon.  That
should be less of a problem.  When shooting the moon, remember to
expose using the same settings as you would use for a noontime
exposure on earth, because it will be daytime on the moon.  One can
use the "sunny sixteen rule," i.e., shoot at f/16 and a shutter speed
of the reciprocal of your film's ASA.  If you wish to quibble, this
assumes that the moon is a standard Kodak 18%-gray card, when
actually the moon's albedo is only 7%, so you might be excused for
opening up one stop; but I have had best results playing the straight
'sunny sixteen rule."
--Paul S. Boyer   <boyer@xxxxxxxxxxxxx>


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