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

[PhilB]

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.

[Whitters]

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]

Old, but much, much wiser...