Binoculars & Telescopes

Refractors, reflectors and the mount underneath them:

the width of the lens or mirror decides what a telescope shows, not the magnification printed on the box, and a small tube sold on hundreds of power is selling a blur. A refractor’s sealed lens tube needs no upkeep and gives crisp views of the Moon and planets. A Newtonian reflector gathers light with a mirror and gives more aperture for the money, at the cost of an occasional realignment. A Dobsonian is that reflector on a plywood rocker base you push by hand: the most light per dollar, and the bulkiest. Schmidt-Cassegrains and Maksutovs fold the light into a short tube and usually ride on a computerised GoTo mount. An alt-azimuth mount moves up, down and sideways. An equatorial mount tracks the stars once it is aimed at the celestial pole, which long exposures with a body from photo cameras need. From Panama that pole sits just above the horizon, and several popular equatorial mounts cannot tilt down that far on their standard tripod, so check the latitude range in the manual first.

Binoculars for a rolling deck and for the night sky:

roof-prism pairs are slim, straight and easier to seal against spray; the wider kind, with offset barrels and a zigzag body, gives more brightness for the money. On a boat out to the humpbacks off Isla Iguana, a modest magnification with wide front lenses stays steady enough to follow a breach, and marine models add a compass, nitrogen filling and armour for a wet deck. Canon and Fujinon make image-stabilised pairs that cancel the shake at higher power.

Beginner scopes, GoTo scopes and the ones left in a closet:

a first telescope worth having runs from about $100 for a small refractor to around $350 for a reflector on an equatorial mount, and GoTo scopes start near $600. Glass and mirrors do not wear out, so a used telescope loses value because its owner gave up, not from wear. Beginner scopes abandoned after a few cloudy nights change hands for $40 to $100, while a working GoTo scope with its hand controller holds far more of its price.

Mirrors, hand controllers and fogged prisms:

shine a torch down a reflector’s tube. Dust and specks barely touch the view; a dull, milky or peeling coating means recoating. A Newtonian that arrives out of alignment is normal and fixed in minutes with a collimation cap. Power up a GoTo scope and make both axes slew, because the hand controller is the expensive part to replace. Count the eyepieces and the finder, and shake the tripod. With binoculars, fog or droplets inside mean the seals have gone. At arm’s length, look at the circles of light in the eyepieces: round and bright means good prisms, squared off with grey edges means cheaper glass, and a premium badge over square circles is a reason to doubt the badge. Red ruby-coated lenses mark toy-grade optics.

Aperture, eyepieces and the hand controller in the listing:

copy the aperture and focal length from the label on the tube, name the mount type and list each eyepiece by the marking on its barrel. Photograph the mirror or lens lit by a torch and say whether the electronics and power supply work. For binoculars, give the figures engraved near the eyepieces and say whether they are waterproof. Offer to set a telescope up at dusk so a buyer sees it on a real target. Anyone collecting a Dobsonian should come with the back seat folded down: the tube travels lying flat and the base goes in separately.

FAQ:

• Can I take photos through a telescope?

  Of the Moon and planets, yes, with a clamp that holds a phone over the eyepiece. Nebulae and galaxies need a tracking equatorial mount and a camera body fitted with a T-ring in place of the eyepiece; old SLRs from film cameras take the same rings.

• Is the sun filter that came with an old telescope safe?

  No. Filters that screw into the eyepiece can crack from the focused heat. Look at the Sun only through a certified solar filter covering the whole front of the telescope.