"Robert Morein" wrote in message
...

" wrote in message
ink.net...
A while back I was teasing Morein about getting some measurements wrong
with
respect to a telescope. Actually the Hubble telescope.

Mikey, I had the diameter of the telescope wrong.

However, Mr. Allison is incorrect about the use of the pinhole light
source.
He states, "A pinhole CANNOT, under ANY circumstances, create ANY
approximation of a parallel beam unless it is placed approximately an
infinite distance away."

However, the Focault knife-edge test has been used as a method of
examining
the figure of a mirror for hundreds of years. If the mirror is perfect, a
pinhole source placed at the focus of the mirror will cause a reflection
in
the form of a parallel beam.

http://www.answers.com/topic/amateur-telescope-making


Except your own reference doesnt show the pin hole light source
as anything close to parallel. Perhaps with the addition of the proper
mirror a pin hole light source can be converted to parallel, but
your reference doesn't even show that.

Bob, I'm starting to worry about you. Are you under anyones care?

ScottW