Advantages of reflecting telescopes over refracting telescopes


	Advantages of reflecting telescopes over refracting telescopes
	Advantages Not prone to chromatic aberration as no refraction occurs. Mirrors can be supported underneath so they don't distort as much as lenses (which can sag under their own weight due to gravity, and can only be supported on their edges). Large mirrors of good quality are much cheaper to build than large lenses of good quality as removing impurities such as gas bubbles from lenses if difficult and expensive. Used in radio (parabolic dish gathers light and focuses it on an antenna --> high gain amplifier --> tuner to select wavelength --> computer for false colour image), IR (which needs to be cooled), X-ray (with skimming mirrors and a mesh/ccd) and UV telescopes.	Disadvantages Secondary hyperbolic convex lens blocks out a small portion of the light. Prone to spherical aberration if primary concave mirror is not perfectly parabolic.
	Evaluation

Not prone to chromatic aberration as no refraction occurs.
Mirrors can be supported underneath so they don't distort as much as lenses (which can sag under their own weight due to gravity, and can only be supported on their edges).
Large mirrors of good quality are much cheaper to build than large lenses of good quality as removing impurities such as gas bubbles from lenses if difficult and expensive.
Used in radio (parabolic dish gathers light and focuses it on an antenna --> high gain amplifier --> tuner to select wavelength --> computer for false colour image), IR (which needs to be cooled), X-ray (with skimming mirrors and a mesh/ccd) and UV telescopes.

Secondary hyperbolic convex lens blocks out a small portion of the light.
Prone to spherical aberration if primary concave mirror is not perfectly parabolic.

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