By the time that William Herschel embarked on his career in astronomy, the telescope had been in use for over 160 years. Progress in improvement and refinement of the instrument had been painfully slow, however, with a combination of factors responsible for the circumstance.

The primary problem with the refractor telescopes of the seventeenth and eighteenth century was spherical and chromatic aberration, a result of the fact that these were single lens instruments that could not overcome their inherent faults. The solution that was found was to increase the focal lengths of the instruments. Where the simple Galilean telescopes of the mid-seventeenth century had apertures of under 2 inches and focal lengths of 2 or 3 feet, instrument makers found that increasing the focal lengths by a factor of 5 or 10 times helped reduce the effects of the aberrations, though they were not nearly eliminated. Over the course of the succeeding decades, astronomers began using telescopes with focal lengths of well over 100 feet and in some cases over 200 feet. Not surprisingly, these were clumsy and cumbersome instruments to use; it was difficult enough aiming the telescope at a selected object, let alone following the object across the sky for any length of time. It was only in the mid-eighteenth century when the first achromatic telescopes were developed that the long refractor telescopes passed into history.