One Sun, 2 Apr 2000 22:55:51 -0400 "Stewart Dean" <sdean@xxxxxxxxxx> wrote:
Something that isn't obvious is that all our beautiful lenses are just
junk in space....'cause the careful design that went into them, all the
corrections, etc. are based on a glass to air interface....which is NOT
the same as a glass to vacuum interface. An old friend of mine
worked on the redesign of the Hasselblad lenses that were used in the
space program: one-offs for glass to vacuum. Think of the cost!
Index of refraction of vacuum: 1.0
Index of refraction of air at STP (760mm/20C):1.00029
Difference those three parts in 10,000 are going to make to pictures: nil.
You might have a slight shift in focal length, but general lens performance
should be almost entirely unaffected, because the fancy work is done
by interfaces between glass and glass.
Getting out my old vacuum handbook I can see a bunch of other reasons
why space-qualified lenses would have to be one-offs -- you don't
want outgassing
of lubricants, sealers or cements, and you probably want to modify
the lense to that all of its internal spaces either are sealed or
else vent properly to space to prevent condensation, dust-sucking and
other unwanted behavior. (That's in
addition to the obvious glove-rated stuff).
paul
--
Paul Wallich pw@xxxxxxxxx
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