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Originally Posted by glenc
William Herschel calculated that a new speculum mirror absorbed 33% of the light and hence it reflected 67%. [1] Aluminium mirrors reflect 89% of the visible light. [2] This means Herschel's 18.3” had the same magnitude limit as a 15.5'' aluminium mirror assuming there was no secondary in Herschel’s telescope. So todays 16" should show all the faintest Herschel objects but may not resolve as well.
[1] The History of the Telescope. King p. 137.
[2] King p. 382. |
We will also give them a try in Peter Robbins 30" (robbo"s 30) on the 23rd this month at Cambroon Weather permitting.
