RE: ATM Baffling a newt - street light tests

[Andrew.Martyn@dao.defence.gov.au]

About 6 months ago I turned my closed tube telescope into an open design to
reduce weight, tube currents and movement by wind. I achieved all those
things but had a problem with stray light. With some investigation I found
the problems was that the diagonal could see for a few degrees outside the
the framework of the open tube. Thus any light object just outside the line
of the tube would could be seen at the focal plane. It is easy to check by
removing your eyepiece and looking down the focuser to see if you can see
anything but the mirror and any light shield you have round the mirror. If
you can see the ground or anything that is not black you have got a
problem. I fixed this problem and I now only get slight degredation when I
shine a torch down towards the mirror which I believe is due to whatever
light reflects off the blackened surrounds of the mirror.

Andy Martyn
Canberra
Australia