Re: ATM 11.2" F/2 Primary testing questions :)

[Dominic-Luc Webb molmed <Dominic.Luc-Webb@molmed.ki.se>]

On Tue, 1 Jan 2002, Nils Olof Carlin wrote:

   > One test that has been discussed a good deal on this list is the pentaprism test, see archives. The setup could use a laser diode at focus, a moving pentaprism (or two flat mirrors, perhaps small diagonals, suitably mounted), and a small aperture reading refractor with a calibrated grating in the eyepiece.
   > I haven't heard of anybody trying it, but as far as I can guess, it wouldn't be terribly critical mechanically, and not require very expensive optical components, and still offer sensitivity and accuracy second to none. Also, it would test e.g. Cassegrainian optics that are not so easily tested by the common near-COC tests.
   >
   > Or if somebody out there has actually tried it, why not tell us?


Maybe be. Maybe... still looking into this. I had some of my own
ideas with lasers that I will likely abandon. The constuction
did not look too gruesome, and I think you were the one who
described it to me, Nils....


I have some very short focal ratio primaries, short even by James'
definition. I didn't check with the foucault tester, didn't care
either. With curves like F/1.0 and F/1.6, I accept from the sagitta
from a spherometer that I have something very short and very hard to
figure. I will accept *anything* with a good figure, F/0.9, F/1.0 or
F/1.1. The rest of the system is trivial by comparison, and will be
planned around whatever success I have with the primaries.

Failing a parabaloid, I am pretty sure I can get a decent sphere
and will go for a Schmidt.

:)


Cheers,



Dominic

North 59 37' 30"
East  17 48' 10"