Is this ads in the AstroMart was your one? This ads claimed, that due
to constant
unrealistic promises of the original customer to pay the balance, you
decided to
put the ads on the AM for free selling?
As I remember, this was at the end of the year 2004.

As for 21" - flag in your hands! But I don't beieve, that if it will
be triplet, it will
work under the real sky - problems with thermal equilibrium with
enviroment air,
following temperature fall, figure stability due to gravity forces.

IMHO, the limit size of a trouble-free APO will be 16" doublet.
Doublet with OK-4
is a bit problematic because of adequate mate element.
The reason I think so about limit size is that I used 16" F/15 Zeiss
refractor for
several evenings. It tooks about three hours to reach acceptable
figure after the
dome was opened. During evenings with rapid temperature fall, this
refractor never
worked at it's best.


However, I wish you a success with 21" project - may be I will have a
chance to
look through it during next Mars apparition.

VD