Refractor vs Reflector vs Schmidt-Cassegrain: Which Telescope Type?
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Every telescope does the same job, gathering light and focusing it, but there are three common ways to do it. Definitions below are from Celestron's astronomy glossary.
Side by side
| Refractor | Newtonian reflector | Schmidt-Cassegrain | |
|---|---|---|---|
| How it works | Front lens focuses light straight back to the eyepiece | Primary mirror at the back; small flat secondary sends light out the side | Corrector lens plus two mirrors fold the light path |
| Upkeep | No mirrors to align | Occasional collimation (Celestron) | Collimation per maker; Maksutovs never need it (Celestron) |
| Aperture for the money | Less than a Dob (Sky-Watcher) | Highest, for Dobsonians (Sky-Watcher) | Less than a Dob (Sky-Watcher) |
| Size | Long tube | Long tube | Short, compact tube |
| Typical mount | Alt-az tripod | Dobsonian or equatorial | GoTo fork or equatorial |
| Daytime use | Easy with an erect-image diagonal | Awkward (image is flipped) | Possible with a diagonal |
Refractors
Celestron describes the light passing "in a straight line from the front objective lens directly to the eyepiece." Sealed tube, no mirrors to align. The catch is cost per inch: a 100 mm refractor is a mid-size telescope, while 100 mm is a small reflector. See refractor telescopes.
Celestron Inspire 100AZ
- 100 mm refractor (per Celestron) with erect-image optics
- Lens cap doubles as a smartphone adapter, per the listing
- Red LED flashlight stored in the mount head
- Folding accessory tray
Newtonian reflectors
A concave primary mirror "collects and focuses incoming light onto a flat secondary (diagonal) mirror," which reflects it "to an eyepiece on the side of the optical tube," per Celestron. Sky-Watcher says Dobsonians give "the highest possible aperture for their money" compared with Schmidt-Cassegrains or refractors. And aperture matters: Tele Vue's Al Nagler wrote that for faint galaxies and clusters "there is no substitute for aperture." The cost is collimation now and then.
Celestron StarSense Explorer DX 130AZ
- 130 mm (5 in.) Newtonian reflector, per the listing
- Phone dock + StarSense app points you to targets with on-screen arrows
- Manual alt-azimuth mount with dual-axis slow-motion controls
- 2-year US warranty
Sky-Watcher Classic 200 Dobsonian (8 in.)
- 8 in. solid-tube Dobsonian, per the listing
- 2 in. Crayford focuser with 1.25 in. adapter
- 25 mm and 10 mm eyepieces; 9x50 finder
- About 45 lb assembled (20 lb tube, 25 lb base)
Schmidt-Cassegrains (and Maksutovs)
Light enters through a thin corrector lens, bounces off the primary mirror to a convex secondary, then goes back out through a hole in the primary to the eyepiece, per Celestron. The result is a big aperture in a short tube. Celestron says the related Maksutov-Cassegrain design "never needs to be collimated."
Celestron NexStar 8SE
- 8 in. Schmidt-Cassegrain optics, per the listing
- Computerized GoTo mount with NexStar+ hand control; 40,000+ object database
- SkyAlign: center any three bright objects to align
- 2-year US warranty
Which should you pick?
- Want the most to see for the money: a reflector, ideally a Dobsonian.
- Want simple and low-maintenance, or daytime use too: a refractor.
- Want compact with GoTo: a Schmidt-Cassegrain like the NexStar SE.
FAQ
Refractor vs reflector?
Lens up front vs mirror at the back.
Which needs more maintenance?
Newtonian reflectors.
What's a Schmidt-Cassegrain?
A folded mirror-and-lens design in a short tube.