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Here is a thought that I haven't seen mentioned yet to use a standard camera of any type with a zoom lens.
If you can obtain a sphere with a mirror surface or just a half sphere and place it where the whole sky can be reflected off it. Suitable mirrors are available and used for cheap planetariums. Much cheaper than a fisheye lens set up.
The camera is sited to focus on the image of the sky on the sphere. The resulting image will have some distortion but there is a suitable algorithm to process the picture back to a circular 2D picture of the whole sky.
The way I would experiment would be with an old slide projector (zoom lens type) with the lamp assembly replaced with a digital camera like a QHY8 or your web cam for a start.
This idea is the reverse of the process used to illuminate the dome in simple digital planetariums using Stellarium.
See the yahoo.groups small_planetarium group for a source of mirrors
Barry
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