It's time to break the silence with something simple: "The Astro Mod" of Canon EF-50mm 1.8 II!
The EF 50mm 1.8 II is notoriously sloppy, mechanically. It's really good for AF in the cold weather. I've tested it at -30C and seen there is no friction, AF runs smoothly. The drawback is the poor collimation, and it may even change according to the camera orientation. Poor collimation means that the image is not equally sharp throughout the field of view. It should not be a problem for landscape photography, but the starry sky shows the flaws of the optics hands down.
Fill the gap! This is not my design. I was looking for information about 50mm modifications and improvements and then I found this from Jim Riffle's website:
Photo: Jim Riffle, http://www.astroworks.com/gallery/350D/widefield.html
It removes the slackness and it also works as a dew/glare shield. No disassembly required, and there's nothing permament in this addon. Now the manual focus has a decent touch, and it stays where you adjust it, with proper collimation. I don't recommend trying AF as the friction might damage the internal gears.
Here's my first implementation with self-adhesive transparent film, with the protective paper kept on:
Photo: Sami Jumppanen
Now I can focus to the remaining problems in astrophotography: the actual focusing, and aligning and stabilizing the mount. Waiting for some free time and good weather.