Sadly, Nils-Olof passed away on August 14, 2015.
This site is a copy of his original, which no longer exists.
Since April -14 in Onslunda, a small village in the south of Sweden, at 55.60deg N, 14.06 deg E
right now you can find:
When is a center spot on a secondary mirror visible?
The spherical aberration of a paraboloid mirror for objects of finite distance
Mirror edge supports - an attempt to find out just how sensitive they are to small errors of adjustment. You may be surprised how little it takes to cause serious astigmatism or other image degradation in a thin, large mirror.
Some pages about various aspects of collimating Newtonian telescopes:
Some Amateur Telescope Making projects:
My collimation page translated: