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From: lee@srs.UUCP (Lee Hasiuk)
Newsgroups: sci.space,sci.crypt
Subject: Re: satellites
Message-ID: <531@srs.UUCP>
Date: 13 Jan 88 15:26:28 GMT
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Organization: S.R. Systems, Rochester NY
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>    That's true, they don't use cameras, in the sense of a piece
> of film isn't currently used, However, the concept of diffractive losses
> apply to any situation where an image is formed, and light, or in the 
> more general sense, Electromagnetic waves, are passed through an aperature.

Actually, this may not be completely true.  According to the 'The Puzzle
Palace', some reconnaissance satellites have the capability of ejecting
film cannisters which can be picked up by airplanes as they fall to Earth.
This technology was developed in 1960.

> 
>    From Jenkins & White, Fundamentals of Optics p331
> 
>    Minimum angle of resolution in seconds = 1.220 * ( lambda / D )
> 
>    Where D is the diameter of the aperture and lambda is the wavelength
> of the light. It is physically impossible, using 1 image, to get below 
> this limit. 
> For the visible range ( lambda ~ 555 nanometers ) and D = 2 meters,
> theta = 3.39e-7 radians
> For an orbit of 200 miles, features resolve to ~ 5 inches. Not bad, but
> that assumes a perfect atmosphere. 
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> I cannot comment on the possibility of image processing, since 
> I know squat about that topic
> 

In a complex analysis class, we were told that the diffractive 'limits' of
lenses and mirrors could be bypassed to a certain degree through the use
of analytic continuation.  Anyone care to comment?