Every telescope solves the same problem — gathering more light than the human eye can on its own, and bending that light to a sharp focus — but the two classic designs solve it in different ways. Understanding the difference explains most of what you'll read on a spec sheet.
Refractors: bending light with glass
A refractor uses a glass lens at the front of the tube to bend incoming light toward a focus point at the rear, exactly like a long, narrow camera lens. Because the light path never doubles back on itself, refractors tend to produce contrasty, sharply defined images, which is why they're popular for lunar and planetary observing. Their sealed tube also keeps dust and air currents out, so the view tends to be free of image degradation from internal turbulence.
The tradeoff is cost and weight scaling: a large, high-quality lens is expensive to produce and grows heavy quickly, which is why refractors rarely go much past 150mm of aperture in amateur instruments without a steep price jump.
Reflectors: focusing light with mirrors
A reflector uses a curved primary mirror at the back of the tube to gather light and bounce it forward to a smaller secondary mirror, which redirects the image out to an eyepiece on the side of the tube (in the common Newtonian design). Mirrors are far cheaper to produce at large sizes than lenses, so reflectors deliver more aperture per dollar — a real advantage for faint deep-sky targets like galaxies and nebulae, where raw light-gathering matters more than pinpoint contrast.
The open tube design does mean reflectors need occasional collimation — realigning the mirrors — and are more exposed to air currents and dust than a sealed refractor.
Which should you choose?
- Want the sharpest, most maintenance-free views of the Moon and planets, and don't mind a smaller aperture for the price → refractor.
- Want the most aperture for your budget, mainly for faint deep-sky targets, and don't mind occasional mirror alignment → reflector.
- Want a compact design with reflector-like light-gathering, at a higher price → look at catadioptric hybrids like the Maksutov-Cassegrain or Schmidt-Cassegrain, which use a combination of mirrors and a corrector lens.
A note on maintenance
Collimating a Newtonian reflector sounds intimidating in writing but is a five-minute adjustment once you've done it a couple of times, usually guided by a simple collimation cap or laser tool. It's a fair tradeoff for the aperture-per-dollar advantage reflectors offer, and it's worth trying before it rules out an otherwise well-suited telescope.