A refracting telescope works by bending light with its lenses. It gathers and focuses the light by using the objective lens to make a small image of the object and using the eyepiece lens to magnify the image.
The lens' curvature also influences the quality of the telescope's images. The size of the image that the lens produces is directly related to the lens' focal length. As the focal length increases, the size of the image also increases. This is one of the refracting telescope's disadvantages since a long focal length means a long telescope. Other disadvantages of the refracting telescope include the inability to transmit all the light since some light is lost to absorption or reflection and large lenses that can be difficult to make.
Galileo created the first refracting telescope using a convex primary lens and a concave eyepiece lens. To enable his telescope to produce as clear of an image as possible, Galileo used math to calculate the distance between the lenses. He was able to see only a small part of the sky at any time, and the telescope produced fuzzy images from spherical aberration. This early telescope magnified objects three times, and his later creations were able to magnify objects up to 30 times.