The Secondary Mirror
Making a 4.25 Inch Dobsonian
Reflector Telescope
Secondary mirrors for Newtonian
reflectors are elliptically shaped.
From a 45 degree angle they look like a circle. These can be obtained at various sites on
the web. The prices are strangely
exponentially related to size. There
are a few free calculator
programs on the web for figuring out how big your secondary should be.
Since the mirror was small, I opted
for a purchased mirror. The common
wisdom is that it is harder to figure a flat mirror than a parabolic one. I'm not convinced however testing this will
need to wait for a future project.