[glenc (Glen)]

It is interesting to compare my 16" GSO scope with William Herschel's 18.5" aperture 20' focal length speculum mirror telescope.
Prior to 22 Sep 1786 Herschel used a secondary mirror and his 18.5" was equivalent to a 13.3" Newtonian.
After that date he observed with no secondary and his 18.5" was equivalent to a 16.3" Newtonian.
I am assuming the reflectivity of speculum is 67% and the reflectivity of aluminium is 93%.

Herschel's 39mm eyepiece magnified 157 times and had a field of 15' 4".
My 13mm EP has a magnification of 138 times and a field of 30'.
So my 16" with a 13mm EP has a similar magnitude limit but twice the field of Herschel's scope.
I am glad my scope is not 20' long, it is much easier to observe with just a small step.

Calculation
(18.5x18.5) x 0.67 = (16.3x16.3) x (0.93x0.93)
single mirror 67% compared with two mirrors 93%

William and John Herschel discovered 3931 DSO with their 18.5" telescope. Most of them (3259) were galaxies.
The rest were 492 open clusters, 48 globular clusters, 82 nebulae and 50 planetary nebulae.