Bare in mind that the Speculums mirrors' reflectance was about 60% and with a speculum secondary brought the total transmission to about 30%. No AR coatings on the eyepieces either. It would have taken a fair bit of aperture to even see the 5th and 6th stars and the slightest mirror aberration they would have vanished.
The vast majority of Herschels scopes were around F13 and only had to be polished spherical although he was known to have made a 24" in later years of F4 focus. Incredible given that the only test available then (before even the foucault test) was to use masks on the mirror and compare the focus point of differnt parts of the mirror on a distant terrestrial scene.
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