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:
På svenska:
Some links:
My collimation page translated: