Collect the information about lenses used by Galileo in his telescope.

Hint: Galileo designed a telescope widely known as a Galilean telescope. It was named after him but the design has no intermediary focus, results in a non-inverted and, with the help of some devices, an upright image. In other words, it was a crude model. Although crude, it did serve as a prototype for the modern-day refractor telescope.

Complete step-by-step solution:
In the Galilean telescope, the objective lens was convex in nature and the eyepiece was concave (whereas modern telescopes use two convex lenses). Galileo knew that light from an object placed at a distance from a convex lens led to the formation of a real image on the opposite side of the lens.
He also knew that if a concave lens were used, the object would form a virtual image on the same side of the lens where the object was located. If moved at a distance, it appeared larger than the object. After a lot of work and different arrangements to get the proper size for the lenses and proper distance between them, Galileo was able to make it work. Even for the various defects and shortcomings, his telescope remained the most powerful and accurately built telescope for decades to come.

Additional Information:
In the nineteenth century, telescopes were used for groundbreaking work on astrophotography and spectroscopy. Galileo’s initial prototypes for the telescope only magnified up to eight times but he soon refined it to provide twenty times magnification. The main problem with his telescopes was the very narrow field of view, typically about half the width of the Moon. Because of the aforementioned flaws in the design, the images were distorted and out of focus.

Note: Despite the flaws, Galileo’s telescope was still good enough for scientists to explore the sky. It was used to view craters on the Moon, the four largest moons of Jupiter, and the phases of Venus. Furthermore, with modifications in Galileo’s design, early refractors were used to discover the largest moon of Saturn, Titan, as well as three more of Saturn's moons.