The earliest working telescopes was made around 1608 with many who claimed its discovery. The design was simple; a convex objective lens and a concave eyepiece allowed the user to see further. In 1655, astronomers had build more powerful telescopes using a design by Kepler. This design used a convex objective lens and a convex eyepiece lens. In 1668, Isacc Newton created the first working reflector to reflect the light to a eyepiece on the side of the telescope, similar to modern day telescopes.
Then with the production of larger paraboloidal mirrors in 1721, the process of coating mirrors with silver in 1857, and the usage of aluminized coating in 1932 further modernized the telescope.
Compared the jump in technology from 1608 to 1900s with the large leap of advances from the 1900s to present day and you will understand how fast technology has grown recently and the speed it is going for the future.