An optical telescope is a telescope that is used to gather and focus light mainly from the visible part of the electromagnetic spectrum. The optical telescope allows the user to directly view a magnified image of something far away. The term is used especially for a monocular with static mounting for observing the sky.
There are three primary types of optical telescope:
* Refractors which use lenses
* Reflectors which use mirrors
* Combined Lens-Mirror Systems which use both lenses and mirrors
The basic idea of an optical telescope is that the primary light-gathering element - the objective lens or the concave mirror - focuses light from a distant object to a focal plane where it forms a real image. This image can be recorded with a camera or simply viewed through an eyepiece which acts like a magnifying glass. The naked eye sees a magnified virtual image that is a very long way away.
Telescopes that have two convex lenses causing the image to appear inverted. Terrestrial versions of such telescopes employ prisms or a relay lens between the object and the eyepiece to invert the image again making it appear as it truly is thus an upright image appears […]

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