It's been quite some time since I've bought a book about telescope making: I just have been more absorbed in the world of amateur radio lately. Still, on my trip to Portland, I noticed that James Daley had published a book on an unusual telescope: the Schupmann.
The Schupmann is an unusual telescope in that it is a refracting telescope with nearly perfect correction for chromatic aberration without using any exotic glasses. The main objective lens is a simple single element lens, which has a considerable amount of chromatic aberration. To cancel out this aberration, the light path is passed through a Mangin mirror: a meniscus lens where the back surface is coated with a reflecting coating which turns it into a second surface mirror. By carefully balancing the power of each of these elements, you can cancel out the chromatic aberration of the main lens. It's a remarkable design, and rather uncommon. The only one I had seen was Jerry Logan's superb 7" instrument at the Riverside Telescope Maker's conference.
Here are some links to the associated patent:
Well, what would Christmas be without a link to that classic of classics: the immortal Dickens' tale A Christmas Carol. This version is illustrated to boot. Nifty.
I'm interested in mapping and in open source, so it's interesting to see projects which combine both. Such is OpenStreetMap, a project which not only produces software to use maps, but also relies upon user data to create maps that can be used freely. I heard about this a while ago, but today it came to my attention again, and I must admit: the data looks pretty good! Check out this map of the bay area:
Addendum: The map above just links to some tiles that are mantained on the OpenStreetMap website, and rendered by Mapnik, which is a toolkit for rendering maps. If you wanted to, you could render many different style maps using Mapnik: check out their documentation.
Addendum2: Tim O'Reilly wrote up some more about it.