Reflecting telescope
Intermediate
Uses a concave mirror.
Uses a large concave mirror as objective, avoiding chromatic aberration and allowing very large apertures with a lightweight support. The Hubble and Webb use mirrors.
Webb's mirror is 6.5 m across.
Needs a secondary mirror to bring the image out.
In more detail
A reflecting telescope uses a curved mirror as the objective, avoiding chromatic aberration and allowing large apertures. Newton's design uses a flat secondary mirror to direct the image to the eyepiece.
Real-world uses
- Large observatories use reflecting telescopes, such as the Keck and Hubble telescopes.
- Amateur telescopes often use Newtonian reflectors.
- Large observatories use reflecting telescopes with concave mirrors, which avoid the colour problems of big lenses.
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Frequently asked questions
Why use mirrors instead of lenses?
Mirrors have no chromatic aberration and can be made much larger.
What is the main drawback?
The secondary mirror and support structure can block some light and cause diffraction patterns.
Why are mirrors preferred for big telescopes?
Mirrors do not suffer from chromatic aberration and can be supported from behind, so they can be made much larger than lenses.
Related topics in Optics
Simple microscope · Compound microscope · Astronomical telescope · Camera and f-number · Wave theory of light · Huygens' principle