(BllFs6) wrote in message ...
He told me that these objectives
are polished to 1/20th wave after the 3rd polish.

Well

Given that a REFRACTING surface effects the wavefront roughly 1/4 as strongly
as a mirror surface.....this means that any given refracting surface that hase
1/20 th wavefront error is roughly that of a 1/5 wavefront error mirror in
terms of absolute surface accuracy requirements.....and given moderate,
spherical surfaces.....the claims may be slightly exaggerated but the are not
neccessarily "astronomical"

Blll


Blll,

It is clear, that lenses were _polished_ to 1/20 wave (guess surface
accuracy). That mean, wave front for each lens is about 1/30 wave
P-V. Complete objective (if it is a doublet) will has about 1/25 wave
wave front P-V.

Ask any refractor manufacturers out here and there if they can make
such precision in 5" objective for... about $200 (dealer's profit included).
Ask them if they can support such quality in general.

I think, that they will only smile in answer.


Valery Deryuzhin.