A refracting telescope uses a lens as its objective to form an image. The refracting telescope was designed for used in a glass glass, but is also used in other devices such as binoculars and telephoto camera lenses.
There are two principles to a refracting telescope, an objective lens and an eyepiece. These two principals gather more light for the human eye and helps to focus and present it in a brighter, clearer, and magnified virtual image. A refractive telescope bends light to cause parallel light rays to converge at a focal point.
Galilean Telescopes are refracting telescopes. Galileo came up with the design in 1608 and uses a convex lens and a concave eyepiece lens. The Galilean telescope magnifies objects up to thirty times. The Galilean telescope was the first telescope to see the planet Jupiter and its moons.
The Keplerian Telescope, invent by Johannes Kepler in 1611 improvements upon Galileo's design. The Keplerian Telescope uses a convex lens in opposition to Galileo's concave lens. This allows for a broader field of view and greater eye relief. However, the view is introverted.
An achromatic refractor is a refracting lens which was invented in 1733. The design over came the need for very long focal lengths and used two pieces of glass with different dispersion to limit the effects of chromatic and spherical aberration. Each side of each piece of glass is ground and polished, at which point the two pieces of glass are assembled together. Achromatic lenses bring two wavelengths together and focus them on the same plane.