Re: ATM Big Bad Cheap Lenses?

["Bob May" <bobmay@nethere.com>]

If an image guide is what you need (ala a periscope), a pair of telescopes
of low power back to back and focused at infinity is basically what you
want.  The first telescope turns the light into a small beam of parallel
light again and the second one turns it back to the large size if the
distance is fairly short.  You do run into viewing angle problems with this
and that won't be changed by anything but multiple inversions of the beam as
it goes down the tube by lenses which reimage the focal plane of the first
lens.  Once you get the light into a 1" to 2" diameter beam, this sort of
stuff can be done a lot easier than with the larger 8' to 12" beam.  The
inversions are to keep the beam near the center so that large optics won't
be needed.  Simple geometry works well for describing what's going on so
simple geometric raytracing will work just fine.
Visiting sites like the Edmund Sci. website and perusing the optical
explainations will probably help in figuring out what you need.
I'd probably start with a Fresnel lens of about 1 meter FL and put a
moderately long FL lens of about 2" diameter in series to reimage the light
as often as is necessary to bring the light to the focal plane of the second
large lens.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net