This is the design of diagonal support I have always used, using three
hacksaw blades. It is incorporated into the top end ring of the tube.
Carbon steel hacksaw blades are needed as they can be drilled. It was
pointed out to me that the diagonal mirror was too close to the end
of the tube and would dew up and be affected by stray light. Dewing
is not a problem in Cairns. Anyhow I made the tube longer and changed
the spider fixing. This is illustrated in the second drawing. Another
modification was made, instead of the brass sleeve to hold the diagonal
mirror in place. The dimensions on the drawing are for the tubes and
focussing units I was using.
Though this eliminates the spikes on star images, an observer has told
me that six small spikes are evident on the outer field on high magnifications.