What are a compound scope’s virtues?. Compound telescopes use a combination of lenses and mirrors to fold a physically long refractor into a lightweight and highly transportable package – very helpful if you don’t have much room to store a big telescope. The light-gathering lens is at the front of the short optical tube and the eyepiece is at the rear – similar to a conventional refractor, but much shorter in length. Compound scopes are almost completely free of the coma found in reflectors and the chromatic aberration found in refractors. Stars are essentially point-like and coma-free across the visual field of a compound scope. There’s no trace of colored halos around bright stars and planets to mask faint details and colors.
The compound scope’s drawbacks? They don’t have as wide a contrast range on the Moon and planets as a refractor, because of the light scattered by the secondary mirror, nor can they split binary stars as cleanly. Because they have small light-gathering apertures, they are dimmer than larger reflectors in a similar price range.
These drawbacks aside, if you don’t have room for a big scope, a compound may well be the right starter scope for you.
Here are a pair of compound scopes that make good first telescopes: Bushnell NorthStar 3.5” computerized go-to altazimuth and Konus K90MAK 3.5” equatorial.
COMPOUND SCOPE REPORT CARD
(used in excellent seeing conditions and with no light pollution; adapted from Astronomy Magazine):
| E = excellent | VG = very good | G = good |
F = fair
| P = poor | Small aperture compound scopes: | 0
| | Portability: | E | | Ease of setup: | VG | | Ease of
use: | G+ | | Performance on the Moon: | E | | Performance on comets: | F | | Performance on
double stars: | G |
| Performance on galaxies and nebulas: | F | | Performance on
planets: | G |
|
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What are a compound scope’s virtues?. Compound telescopes use a combination of lenses and mirrors to fold a physically long refractor into a lightweight and highly transportable package – very helpful if you don’t have much room to store a big telescope. The light-gathering lens is at the front of the short optical tube and the eyepiece is at the rear – similar to a conventional refractor, but much shorter in length.