The three families
Refractors bend light through a lens at the front. Sealed, collimation-free, no central obstruction — and the most expensive design per millimetre of aperture by a very wide margin.
Reflectors collect light with a mirror and bounce it out of the side of an open tube. By far the cheapest aperture available, at the cost of routine collimation, a central obstruction and bulk.
Compound (catadioptric) telescopes use both a lens and mirrors to fold a long light path into a short tube. Compact and versatile, with a larger obstruction and a long cooldown.
The comparison that matters
| Refractor | Reflector | Compound | |
|---|---|---|---|
| Cost per mm of aperture | Highest | Lowest | Middle |
| Collimation | Never | Regularly | Occasionally |
| Cooldown | Minutes | 20–60 min | 45–90 min |
| Central obstruction | None | 20–25% | 30–45% |
| Widest field | Widest | Wide | Narrowest |
| Tube length for a given focal length | Longest | Long | Shortest |
How to choose between them
Choose a refractor if you want zero maintenance, instant readiness and the cleanest possible image of bright objects, and you accept that your aperture will be small for the money. This is also the default for wide-field astrophotography, where small aperture is not the handicap it is visually.
Choose a reflector if aperture is what you want and you are willing to collimate. For visual deep-sky observing this is not a close contest: the money that buys a 100 mm apochromat buys a 250 mm Dobsonian.
Choose a compound telescope if you need a long focal length in something you can carry, or you want one telescope that does planets, deep sky and imaging competently. This is the design that makes complete GoTo packages practical.
The contrast argument, settled as far as it can be
An unobstructed refractor preserves mid-frequency contrast that a central obstruction removes. This is why a 100 mm apochromat can look “cleaner” on Jupiter than a 200 mm Schmidt-Cassegrain.
The Cassegrain is nonetheless resolving twice as much detail. Both observations are true, which is why the argument has run for fifty years without resolving.
The practical version: in poor seeing, the smaller cleaner image often looks better. In good seeing, aperture wins and it is not close. If you observe from a site with habitually turbulent air, that tilts towards smaller and cleaner. If you get steady nights, it tilts towards aperture.
What this choice is not about
Optical quality. Mainstream products from all three families are made to similar standards. Differences between individual samples are usually larger than differences between designs.
“Professional” designs. Research telescopes are all reflectors, for reasons of scale and cost that have nothing to do with what works in a back garden.
Brand. Most of these telescopes come from a small number of factories regardless of the badge.