Herschelian telescope
A Herschelian telescope was invented in the 1780s by William Herschel. It is similar to a Newtonian telescope, except using only one mirror.
In the 1780s, telescopes used metal mirrors which were not very reflective. Each mirror would absorb light and make the image dimmer. So Herschel invented a telescope with a tilted mirror that put the eyepiece in the front.
When mirrors became more reflective, Herschelian telescopes stopped being useful.
Herschelian Telescope Media
24-inch convertible Newtonian/Cassegrain reflecting telescope on display at the Franklin Institute
A replica of Newton's second reflecting telescope which was presented to the Royal Society in 1672.
An image of Sirius A and Sirius B by the Hubble Space Telescope, showing diffraction spikes and concentric diffraction rings.
Main mirror of James Webb Space Telescope assembled at Goddard Space Flight Center, May 2016.
Light path in a Gregorian telescope.
Light path in a Newtonian telescope.
Light path in a Cassegrain telescope.
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