Binoculars & Telescopes

Pocket pairs, marine binoculars and tripod pairs:

the two numbers printed on every pair are the magnification and the width of the front lenses in millimetres. Pocket pairs slip into a bag but go dim at dusk; full-size pairs are the all-rounders. Marine binoculars keep to low power and wide lenses, because that holds the image calm on a rocking deck, and good ones are sealed and gas-filled so they never fog inside. Big astronomy binoculars show the craters on the Moon but need a tripod. For watching a gate all night, a fixed camera from security and surveillance does the job better than a night-vision monocular.

Telescopes and the mount under them:

a refractor has a lens at the front and needs almost no care; a reflector uses a mirror at the bottom of the tube, gives more aperture for the money and needs lining up now and then. First-time owners blame the optics when the real fault is the mount: a light tripod that shakes at every touch ruins any tube. GoTo mounts find objects for you, and smart telescopes such as the ZWO Seestar skip the eyepiece and build the picture on your phone. To photograph the whales rather than watch them, a long lens from photo cameras beats a phone held to an eyepiece.

The magnification sticker and the zoom binocular:

magnification is what cheap optics sell on, and it matters least. A telescope can only use so much power before the image turns dim and shaky, and that limit is set by the width of the lens or mirror, not by the eyepiece, so a small tube in a box promising magnification in the hundreds is describing an image nobody will ever see. On binoculars the prisms tell you more: hold a pair at arm’s length towards a bright sky and look at the circles of light floating in the eyepieces. Round and evenly lit means BaK-4 glass; squared off with grey edges means cheaper prisms.

Quetzales for a first pair or a first scope:

a full-size pair from a known optics brand such as Celestron or Bushnell is around Q500 new, and a small manual refractor runs from about Q2,000 to Q2,500. A computerised telescope costs roughly four times that, and nearly all of the difference sits in the motors and the hand controller. That sets the used price: binoculars have almost nothing that wears out, so a clean pair with its case keeps most of its value, while a used GoTo scope is worth what its electronics still do, and one that will not power up is a manual telescope on a heavy tripod.

Salt, grit and the SUN filter in the box:

spray from a season on the boats does the damage. Turn the focus wheel end to end: it should move smoothly with no grit, and the hinge should hold its setting. Shine a torch into the front lenses and look for haze or droplets on the inside, which on a sealed pair means the seals have gone. On a reflector, light up the tube: dust on the mirror is harmless, a milky or peeling coating is not. On a GoTo model, watch it power up and slew. If the box holds a small dark filter marked SUN that screws into an eyepiece, throw it away: those can crack from the heat, and only a proper filter covering the front of the tube is safe for looking at the Sun.

The figures on the tube and the eyepieces in the case:

photograph those rather than repeating the magnification on the box, and for binoculars copy the figures from the body and say whether they are waterproof. List the tripod, finder and any phone adapter, plus the power lead and hand controller on a computerised scope. Someone coming from Salamá or Sanarate will want to look through it before paying, so meet where there is a long view, or on a clear evening with the Moon up. If the scope was a present that saw the sky twice, say so: that is the one buyers hope to find.