Re: A Schiefspiegler as first telescope (was Re: ATM 3-Vane or 4-Vane Spiders)

[mjc5 <mjc5@psu.edu>]

	I suggest the 8 inch f6 or f8. I've made an F10.2 mirror, and it isn't
as easy as it may seem at first. A sphere at that length is a shallow
creature indeed.

	Then if you want to make your Schief, you can apply what you learned
from your first mirror.

	- Mike -

	

Ernest Tomlinson wrote:

> Now everything I've read suggests that the easiest first mirror to attempt
> making is a 6" or 8" medium-focus (f/6 to f/10) parabolic mirror for a
> Newtonian.  The Schiefspiegler requires a sphere of f-ratio at least f/15.
> (I played with Jose Sasian's TCT program to test to see what happened
> if the f-ratios of the mirrors were reduced to f/12; the astigmatism and
> coma
> of the resulting scope seems to me too great.)  There's also the added
> complication of figuring the convex mirror.
> 
> So, what do you all think--is it a valid first project, or should I embark
> on
> something simpler to start out with?
> 
> Ernest Tomlinson.