Telescopes & Mounts
Reflector Telescope
Mirrors instead of lenses — the most aperture per unit of money, at the cost of collimation.
Specifications
| Typical aperture | 114 – 400 mm |
|---|---|
| Typical focal ratio | f/4 to f/8 |
| Optical design | Newtonian — parabolic primary, flat secondary |
| Central obstruction | 20 – 30% of aperture diameter |
| Common focuser | 2″ Crayford or dual-speed |
| Weight (200 mm) | 9 – 13 kg (OTA only) |
Observing parameters
| Useful magnification range | 0.5× – 2× aperture in mm (200 mm → 100×–400×) |
|---|---|
| Practical low power | 30×–60× — richest-field sweeping |
| Practical high power | 150×–300× — planets when seeing allows |
| Typical limiting magnitude | mag 13.5 (200 mm, dark sky) |
| Dawes limit (200 mm) | 0.58 arcsec |
Overview
A Newtonian reflector collects light with a parabolic primary mirror at the back of the tube and bounces the converging cone sideways to an eyepiece near the front. Mirrors have no chromatic aberration at all, and a mirror only needs one optically worked surface, so a reflector gives far more aperture per pound than a refractor of the same price.
The trade is maintenance. The two mirrors must be kept in collimation — aligned to each other and to the focuser axis — or the image softens asymmetrically. A reflector also has an open tube that collects dust, and a secondary mirror held by thin vanes that produces the familiar diffraction spikes on bright stars.
A 6-inch or 8-inch Dobsonian is the standard advice for a first serious telescope for exactly this reason: enough aperture to show structure in galaxies under a dark sky, on a mount that takes ninety seconds to set up.
Where it fits
Practical notes
- Collimate before every serious session; a Cheshire eyepiece or laser collimator takes two minutes and is the single biggest image-quality lever.
- At f/4 or faster, collimation tolerance tightens to a couple of millimetres — a coma corrector also becomes worth having.
- Let the mirror cool: a warm primary carries a boundary layer of turbulent air that destroys fine planetary detail.
- Never clean a mirror to remove dust. Dust costs almost no contrast; a cleaning scratch costs real performance.
Pairs with
Related tools
Refractor Telescope
A lens at the front, an eyepiece at the back — the simplest and most robust optical path.
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Catadioptric Telescope
Lenses and mirrors folded together — long focal length in a short, portable tube.
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Barlow Lens
A diverging lens that multiplies the effective focal length of everything behind it.
Eyepieces & Opticsobserving
Observing Chair
Keeps your eye at the eyepiece height — you see more when you are not contorting.
Observing Accessoriesobserving