Telescopes by what they show
How many Messier, Caldwell and Herschel 400 objects each size of instrument reaches from a dark site and from the suburbs, plus telescopes by budget and weight.
Telescopes: choose by what you want to see
The first question is what to look at. Planets and the Moon want a sharp, long-focus telescope such as a Maksutov-Cassegrain or an apochromatic refractor; faint galaxies and nebulae want the largest aperture you will carry, which for most observers means a Dobsonian. Aperture sets how faint you can see and how fine a detail you can split; focal length sets magnification and field of view.
Getting started
Telescope types
Refractors bend light with lenses, reflectors gather it with mirrors, and catadioptrics fold it with both. What each design trades for its strengths.
Telescope performance
Limiting magnitude, resolving power, focal ratio and the magnification ceiling: the numbers that set what any telescope can show.
Refractors
Achromatic refractors
Two-element lenses: cheap, rugged and quick to cool, with a violet halo around bright stars and planets.
Apochromatic refractors
Three-element lenses with ED or fluorite glass: color-free, sharp and light, the standard for wide-field astrophotography.
Reflectors
Newtonian reflectors
Isaac Newton's design: a parabolic mirror and a flat diagonal. The simplest way to get a big aperture.
Dobsonian telescopes
A Newtonian on John Dobson's rocker box: the most aperture for the money and the usual first deep-sky telescope.
Catadioptrics
Schmidt-Cassegrains
An 8-inch aperture in a tube about 17 inches long, the Celestron and Meade standard for portable, all-round telescopes.
Maksutov-Cassegrains
Small, sealed and sharp, with long focal ratios suited to the Moon, planets and double stars.
Schmidt-Newtonians
A corrector plate on a fast Newtonian for a wider, flatter field.
Research and imaging designs
Ritchey-Chrétien
Two hyperbolic mirrors free of coma: the design of the Hubble Space Telescope and most professional observatories.
Harmer-Wynne
A corrected Cassegrain for flat, wide photographic fields.
Binoculars: the best first instrument
A pair of 10x50 binoculars reaches 88 of the 110 Messier objects from a dark site, costs less than most eyepieces and needs no setup. The first number is magnification, the second the width of each objective lens in millimeters.
Binoculars for astronomy
What binoculars show, from the Pleiades and the Andromeda Galaxy to the moons of Jupiter, and how to hold them steady.
Binocular models
Models and prices for astronomy and birding, from 7x50 to giant 25x100s.
Spotting scopes
Angled and straight spotting scopes for the Moon, planets and daytime birding.
Mounts and tracking: payload decides everything
A shaky mount wastes a good telescope. Alt-azimuth mounts move up-down and left-right; equatorial mounts tilt one axis to the celestial pole so a single motor can follow the stars, which long-exposure astrophotography requires.
Telescope mounts
Alt-azimuth, Dobsonian, German equatorial, fork and harmonic-drive strain-wave mounts, sized by payload.
Tracking and drive systems
Clock drives, GoTo, polar alignment and autoguiding: keeping up with the turning sky.
Eyepieces and filters
The eyepiece sets the magnification: telescope focal length divided by eyepiece focal length. Filters cannot make a sky darker, but they can pass the light of glowing gas and block city lights, or add contrast to the bands of Jupiter.
Eyepieces
Pick them by exit pupil, not by magnification: Plössl, wide-field and ultra-wide designs, and how many to own.
Telescope filters
What filters can and cannot fix.
Solar filters
White-light film and glass filters, and hydrogen-alpha telescopes for prominences. Safety first: only a full-aperture solar filter makes the Sun safe to view.
Accessories: what you need on the first night, and what can wait
A red flashlight, a star chart or app, and a way to keep the optics dry come before any upgrade.
Telescope accessories
Finders, diagonals, Barlow lenses, collimation tools and cases, in the order you will need them.
Dew control
Why optics dew up before the grass does, and how dew shields and heater straps stop it.
Astrophotography: the kit each target needs
The Moon and planets need a fast video camera and a long focal length; nebulae and galaxies need a tracking mount, a short fast telescope and hours of total exposure. Smart telescopes such as the ZWO Seestar and Vaonis Vespera put both in one box.
Astrophotography
From a phone on a tripod to a cooled camera on an equatorial mount: the kit for each kind of target.
Astronomy cameras
CMOS and CCD sensors, cooled and uncooled, mono and color: the sensor matters more than the brand.
Astrophotography software
Capture, stacking and processing, from SharpCap and N.I.N.A. to PixInsight and Siril.