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The Herschel’s Telescope
William and John Herschel used an 18.5” aperture, 20’ long speculum reflector to find DSO. (Speculum metal is a mixture of around two-thirds copper and one-third tin)
Was their telescope better than an 11” refractor? Was it better than a 16” refractor?
One way to find out is to look at the magnitudes of the galaxies they found.
The number of galaxies seen should increase as the magnitude increases.
If it does not increase we have reached a working magnitude limit.
For William Herschel the working magnitude limit was about 13.
For John Herschel the working magnitude limit was about 12.8 or 12.9.
For Heinrich D’Arrest’s 11” refractor it was about magnitude 13.5 or 13.7.
For Lewis Swift’s 16” refractor it was about magnitude 13.7 or 13.9.
They all saw galaxies much fainter than that, but they also missed many that were fainter than their working magnitude limit.
So an 11" refractor was probably better than the Herschel’s 18.5” reflector.
(Or maybe d’Arrest had better eyesight)
The attached table gives some details.
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