For more on mirror objectives, here is an article on using automobile
hubcaps and parabolic L'eggs containers as reflectors.
http://www.versacorp.com/vlink/jcart/allsky.htm
Fisheye photographic lenses are another option, but expensive. Some early
wide-angle camera lenses (for example, the Hill Sky Lens of 1926 for
photographing clouds) used a glass hemisphere as the first lens element.
This evolved into modern wide-angle and fisheye lenses.
http://360vr.com/fisheye41/coastal-fisheyep.pdf
I can envision using a wide-angle lens or mirror to form an image of the
sky, a relay lens to form a second image of the sky in a room below, and a
second reversed wide-angle lens in the room below to project an inverted
image of the sun into the room. More simply, the second image could be
projected onto a grid to show the time.
Gordon Uber
At 22:55 1/8/04, Edley McKnight wrote:
Hi Tom, shadow watchers,
A mirror objective might indeed work. Basically converting the large
angular movement of the sun into a much narrower angle at the top
and then re-expanding the angles at the bottom. This would be a
curved mirror of course, or a set of small mirrors. Approximating it by
a set of small mirrors would probably give insight to the proper
curved mirror required. Essentially focusing all the sun's movement
into a near column down the tube and then dispersing it again at the
bottom. A double curving three dimensional mirror seems like it
would be needed to keep from shadowing itself during part of the
day. Thinking in terms of 'optical levers' might help. Is there an
optical engineer of such caliber on board?
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