This months "Australian sky and telescope " has an article "no tools collimation" which seems to show a simple way of final star collimation . The author describes the out of focus image as having a dark hole near its centre which he alludes to asi the shadow of the secondary. Is it really that ? If so what effect does secondary offset in a fast scope have on its central position? The technique looks so simple and obvious that final collimation of fast newtonians can be easily achieved using it??
Philip
