One of the most informative threads I've ever read, thanks all. Learned a lot on wavelengths, silver, aluminum, coatings here.
Before I re-read it, which 2" diagonal would you recommed for DSO's with a CPC 1100? Especially Galaxies, arms and nucleus, open and globular clusters with and without red giants, and all Nebulae.
A 2" BBHS Mirror, 2" BBHS Prism, 2" Baader Zeiss prism (Discontinued model), or 2" Baader Dielectric?
Do most users still enjoy their BBHS?
Only thing concerning me now is this quote in one of Don's links:
"The reason for going with silver rather than aluminium is a slightly improved reflectivity in the near- and mid-infrared (99.1 per cent at 10 microns), but also that the emissivity of the silver coating is around 38% that of aluminium, which reduces background in infrared observations.
The paper reports on durable coatings that reduces the tarnishing that favours an aluminium coating (as well as aluminium's superior performance shortward of 400nm). I guess that these are rather expensive, so aluminium is still the norm unless you want to be re-silvering the mirror very frequently."
What did he mean by "reduces background in infrared observations and re-silvering the mirror frequently (Will it work for 10 years at least with no polishing required or any discoloration from tarnishing)"?
Have the wavelengths been proven flat from 400nm to 2000nm?
PS> Does this help us visual astronomers at all:
"Nobody has yet mentioned the one aspect of silver that the graph depicts. Silver absorbs strongly near 315 nm. If you were interested in UV light from the stars, you would have a hole in your data (between 310 and 320 nm) if you used silver. Not only that, any light gathered with a wavelength less than 310 nm would require longer acquisition times."
Edited by Procyon, 14 May 2018 - 08:09 PM.