Optical Telescope



An optical telescope is a telescope that is used to gather and focus light mainly from the visible part of the electromagnetic spectrum, this 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 in the eyepiece.

Early versions of the optical telescope often provided blurry images with chromatic aberrations that would put rings of color around bright objects. However, advancements made in the telescope field over the years have all but done away with these flaws and astronomers both amateur and professional alike are now able to see clear images free from distortion.

Almost all large research telescopes are optical telescopes and are reflectors. The reason for this is that for research purposes, the images must be free from imperfection in order for it to be studied accurately. Also, reflectors work in a wider spectrum of light allowing for better imaging.

The term optical telescope almost seems like an oxymoron as 'optical' means with the eye. We can't imagine what other type of telescope there might be that wouldn?t employ the use of the eye for viewing.

However, in technical terms, we must address the fact that the telescope is an optical image device and thus should be referred to as such. Although there are optical telescopes that have cameras attached as well so they are referred to as photographic telescopes.

From large and powerful to small and compact, there are a variety of optical telescopes available to the amateur astronomer.



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