A telescope is an optical tool which gathers and focuses electromagnetic radiation. Telescopes increase the apparent angular size of distant objects, as well as their apparent brightness. Telescopes are usually used for astronomy as well as in many non-astronomical instruments.
Optical Telescope - telescope which is used to gather and focus light, for directly viewing a magnified image or making a photograph, etc.
Light is made up of photons, and professional telescopes concentrate the light onto electronic detectors which collect the photons. There are two primary types of optical telescope:
- Reflector telescope - telescope which uses mirrors to reflect light, rather than lenses to pass light. Nearly all large research-grade astronomical telescopes are reflectors.
- Refractor telescope - telescope which refracts light at each end using lenses. This refraction causes parallel converge upon a focal plane. This can enable a user to view a distant object as if it were brighter, clearer and/or larger.
The word telescope comes from Greek, tele-far and skopein-to look or see, teleskopos-far seeing. The first telescopes may have been Assyrian crystal lenses. Galileo Galilei made his own telescope in 1609 and is generally credited with being the first to use a telescope for astronomical purposes.
No telescope can form a perfect image. Even if a reflector telescope could have a perfect mirror, or a refractor telescope could have a perfect lens, the effects of aperture diffraction could still not be escaped. In reality, perfect mirrors and perfect lenses do not exist, so image aberrations in addition to aperture diffraction must be taken into account.
|
