Author Topic: Tonight, where have the clear skies at 6pm gone?  (Read 4470 times)

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PhilB

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Re: Tonight, where have the clear skies at 6pm gone?
« Reply #45 on: Mar 09, 2011, 06:22:09 »
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

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Re: Tonight, where have the clear skies at 6pm gone?
« Reply #46 on: Mar 09, 2011, 13:48:00 »
Quote
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.
My first scope had a glass prism... Thanks for making me feel sooooo old today.

PhilB

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Re: Tonight, where have the clear skies at 6pm gone?
« Reply #47 on: Mar 09, 2011, 21:34:17 »
Old, but much, much wiser...
“Never worry about theory as long as the machinery does what it's supposed to do.”  Robert A. Heinlein