Image-forming optical system
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In optics, an image-forming optical system is a system capable of being used for imaging. The diameter of the aperture of the main objective is a common criteria for comparison among optical systems, such as large telescopes.
The two traditional systems are mirror-systems (catoptrics) and lens-systems (dioptrics), although in the late twentieth century, optical fiber was introduced. Catoptrics and dioptrics have a focal point, while optical fiber transfers an image from one plane to another without an optical focus.
Catoptrics and optical fiber have no chromatic aberration, while dioptrics need to have this error corrected. Newton believed that such correction was impossible, because he thought the path of the light depended only on its color. In 1757 John Dollond was able to create an achromatised dioptric, which was the forerunner of the lenses used in all popular photographic equipment today.
Lower-energy X-Rays are the highest energy electromagnetic radiation that can be formed into an image, using a Wolter telescope. There are three types of Wolter telescopes  Near infrared is typically the longest wavelength that are handled optically, such as in some large telescopes.