Refracting telescope

A refracting or refractor telescope is a type of optical telescope which refracts light at each end using lenses. This refraction causes parallel light rays to converge at a focal point; while those which were not 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. These are similar to microscopes. The monocular is a type of refractor. A typical refractor has two lenses, an objective lens and an eyepiece lens. The objective lens has two pieces of glass (with different densities), "crown" and "flint glass". Each side of each piece is ground and polished, and then the two pieces are glued together. The curvatures are designed to limit the effects of chromatic and spherical aberration.

Technical difficulties

Refractors are criticized for their relatively high-degree of chromatic and spherical aberration. There is also the problem of lens sagging, a result of gravity affecting glass. There is a further problem of mis-refraction; caused by air bubbles trapped within the lenses. In addition, glass is opaque to certain wavelengths, and even visible light is dimmed when it passes through glass. Many of these problems are avoided by using reflecting telescopes.

Related Topics:
Chromatic - Spherical aberration - Lens sag - Gravity - Glass - Air - Bubble - Opaque - Wavelength - Visible light

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However modern designs using apochromatic optics with low dispersion glass reduce lots of these problems. Such telescopes contain elements of fluorite in the objective elements and produce a very crisp image which is virtually color aberration free. Such telescopes are sold in the high-end amateur telescope market until 150mm diameter.

Related Topics:
Apochromatic - Fluorite

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