• Welcome to Orpington Astronomical Society.
 

News:

New version SMF 2.1.4 installed. You may need to clear cookies and login again...

Main Menu

Tonight, where have the clear skies at 6pm gone?

Started by Fay, Mar 06, 2011, 19:37:21

Previous topic - Next topic

0 Members and 2 Guests are viewing this topic.

PhilB

Quote from: Fay on Mar 08, 2011, 19:40:33
I just wondered where Mick was incorporating a prism in his setup

Back when refractors were routinely of long focal length, around f15 rather than the modern f6, it was common to use a glass prism instead of the modern first surface mirror, in the star diagonal. With the birth of modern 'scopes, the practice fell into disuse due to the high dispersion in such prisms giving rise to 'orrible colour casts in the image.
"Never worry about theory as long as the machinery does what it's supposed to do."  Robert A. Heinlein

Whitters

QuoteBack when refractors were routinely of long focal length, around f15 rather than the modern f6, it was common to use a glass prism instead of the modern first surface mirror, in the star diagonal. With the birth of modern 'scopes, the practice fell into disuse due to the high dispersion in such prisms giving rise to 'orrible colour casts in the image.
My first scope had a glass prism... Thanks for making me feel sooooo old today.

PhilB

"Never worry about theory as long as the machinery does what it's supposed to do."  Robert A. Heinlein