Buying a second-hand telescope

The short answer

• Buys very well used: 150–250 mm Dobsonians, 130 mm tabletop Newtonians, Maksutovs, brand-name binoculars. Simple optics, nothing electronic, and ten minutes shows whether anything is wrong.
• Buy with care: motorised and GoTo mounts (motors, electronics, cables, hand controller — every part is a possible failure and an unobtainable spare), smart telescopes (battery, sensor, updates).
• Never buy used: €99 60–70 mm refractors and 'children's telescopes'. New, they are already bad; the discount changes nothing.
• The fair price: 55 to 65 % of new for a complete instrument in good condition; up to 75 % if it is recent or comes with good eyepieces. Above that, buy new, with the warranty.

The reference price is today's new price, not what the seller paid. This site's pages give the price observed at a retailer, dated; that is the number to have with you.

The models, one by one, with the observed new price

Where to look

In order of preference: the classifieds on astronomy forums, where the seller knows what they are selling, describes the state of the mirror unprompted, and is often selling because they are moving up in aperture. Astronomy clubs, which always have someone parting with an instrument and will let you look through it first. Only then the general classifieds sites, where the best signal is the photo: a tube on a balcony with its cap on, or a tube in a garage with dust on it, are not the same listing.

On general sites, read the listing the way an inexperienced seller wrote it: 'never used' often means 'used once, disappointed' — which is perfect. '525× magnification' in the title means the box is talking, and that is an instrument to avoid new or used.

What to check, in ten minutes

• The primary mirror (Newtonian, Dobsonian): look at it in raking light with a phone torch, without touching it. Dust is normal and changes nothing. A uniform whitish haze is a tired coating: it can be recoated, €80–150, to deduct. Pitted spots or a peeling layer: no.
• The lens (refractor, Maksutov): no scratches, no fungus (a web of white filaments, irreversible), no fogging inside.
• The movements of the base or mount: should be smooth, with no play or jerks. A Dobsonian that sticks then jumps is annoying but fixable (a little Teflon, ten euros); a mount with play in an axis is a mount to replace.
• The focuser: turns without forcing, holds an eyepiece without slipping under its weight.
• What comes with it: at least one eyepiece, the finder with its bracket, the counterweights if there is an equatorial, the collimation screws. A telescope with no eyepiece costs €40–80 more than advertised.
• If you can, look at a star or a distant streetlight at high power: a clean disc either side of focus is good. A comet shape is a mirror out of collimation (five minutes to fix) or, rarely, a bad one.

What to pay

A simple rule, which is a market habit and not a law: 55 to 65 % of the current new price for a complete, clean instrument under ten years old. A 200/1200 Dobsonian at €440 new is therefore worth €250–290 used; a 130 mm tabletop at €220 new, €120–140. Go up to 70–75 % if the instrument is under two years old, if good eyepieces are included (a decent Plössl is worth €40, a wide-field €80 and up), or if the seller delivers. Go below 50 % for a tired coating, a missing eyepiece, or a mount with play.

Binoculars follow the same rule. GoTo mounts lose value faster, because electronics age and buyers know it: 40–50 % of new is common, and justified.

Never pay a used price that approaches a new one on sale. The big models (Skyliner 200P, Heritage 130P) regularly go to −15 or −20 % at retailers, and new comes with a warranty, a fresh mirror and every accessory.

What each budget buys, new

What not to buy used

• The 60/700 or 70/700 refractor on a light tripod, and anything with a magnification in the title. Bad at €119 new, no better at €40.
• The 114/900 or 130/900 Newtonian on EQ1/EQ2 'with motor'. The tube is fine; the mount was already the problem when it was new.
• An equatorial GoTo mount over ten years old with no chance to test it powered up. Hand controllers die, boards cannot be found.
• A smart telescope without a tested battery and a transferred account. The sensor is good for years, the battery is not.
• Any instrument the seller will not let you look at closely. Nobody selling a good telescope has a reason to refuse.

And when it is you selling

Keep the box, the original eyepieces and the receipt. Photograph the mirror in raking light. Sell in spring, when people have seen Saturn at a friend's, not in January, when they are putting theirs away. And say why you are selling: 'moving up to a 250' reassures more than any photo.

The advisor: what to look for, new or used

Questions people ask

Which telescope should I buy second-hand?

A 150–250 mm Dobsonian or a 130 mm tabletop Newtonian: simple optics, nothing electronic, and a fault shows in ten minutes. GoTo mounts and smart telescopes need a powered-up test; €99 refractors are not bought new or used.

How much is a used telescope worth?

About 55 to 65 % of the current new price for a complete, clean instrument, up to 75 % if recent or with good eyepieces. Motorised mounts lose more: 40–50 %.

How do you check a telescope mirror?

In raking light with a torch, without touching. Dust is normal. A uniform haze is a tired coating, €80–150 to recoat. Pits or a peeling layer: do not buy.

Where do you buy a used telescope?

First the classifieds on astronomy forums and the clubs, where sellers know what they are selling. Then the general sites, reading the listing carefully and asking to look through it.

Used 200 mm Dobsonian or new 150 mm Dobsonian?

At the same price, a used 200 in good condition shows noticeably more. The new 150 has the warranty, a fresh mirror and is lighter. If you were able to look through the 200, take it.