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ApertureBuy the right telescope, not the biggest one

The best telescope is the one that gets carried outside.

Most first telescopes are chosen on the wrong number, cost more than they needed to, and are in a cupboard within a year. This site asks eight questions about your sky, your space and your life, and gives you a spending ceiling before it gives you a product.

Quite often the answer is to spend less than you were going to. That is a result, not a consolation prize.

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The number on the box is the wrong number

A 60 mm refractor advertised at “529× magnification” is not lying about arithmetic — 900 mm divided by a 1.7 mm eyepiece really does give 529×. It is lying about physics. That instrument stops being useful at about 120×, and at 529× the exit pupil is 0.11 mm — small enough that you are looking at floaters in your own eye.

Aperture decides how much light arrives and how much detail is resolvable. The eyepiece only divides that up. So every magnification on this site is shown with the aperture it came from and the exit pupil it produces, without exception.

See what a given aperture actually shows →

The instruments

Classes rather than products, because the advice outlives the model numbers. Real models hang off each one.

  • Two small refractors you can hold. The most-recommended and least-bought first instrument in astronomy, and the one most likely to still be in use in ten years.

    5056 mm · 0.9 kg · 1 min to set up

  • A short Newtonian on a small rocker box that sits on a table, a wall or a crate. The best value in astronomy at the moment, and the answer to more first-telescope questions than anything else here.

    100150 mm · 6 kg · 3 min to set up

  • The shape most people picture when they picture a telescope. Sealed tube, nothing to collimate, and a standing eyepiece height that suits sharing.

    7090 mm · 5 kg · 5 min to set up

  • A small motorised wedge that cancels the Earth's rotation, with a camera and an ordinary lens on top. Not a telescope, and the right answer to 'how do I start astrophotography' more often than a telescope is.

    3070 mm · 4 kg · 15 min to set up

  • The most aperture per euro anyone has yet arranged. A full-size rocker box on the floor, a tube you carry in two trips, and views that stop people mid-sentence.

    150200 mm · 20 kg · 8 min to set up

  • A small, very well corrected refractor. Modest aperture bought at a high price per millimetre, in exchange for images with no false colour and a second career as an imaging telescope.

    7280 mm · 5 kg · 6 min to set up

  • A long focal length folded into a short tube, on a mount that finds things for you. The planetary specialist, and the most city-friendly telescope on this list.

    102127 mm · 9 kg · 12 min to set up

  • A small telescope with a camera where the eyepiece would be, driven from a phone. It finds the target, tracks it, stacks exposures, and hands you an image in a few minutes.

    5080 mm · 3 kg · 4 min to set up

  • Where galaxies start having structure and planetary nebulae start having colour. Also where an instrument starts needing a plan rather than a decision.

    250300 mm · 40 kg · 15 min to set up

  • Serious aperture in a tube half a metre long, on a computerised fork. The most capability per unit of storage space, at a price.

    150203 mm · 14 kg · 15 min to set up

  • The real answer to serious deep-sky imaging, and mostly a mount. The telescope on top is the cheap part and the part you will replace least often.

    61100 mm · 22 kg · 45 min to set up

Things that are not true

  • "675× magnification!"

    Useful magnification is capped by aperture at roughly 2× the aperture in millimetres — about 120× on a 60 mm telescope. Past that the image gets bigger and worse: the same light spread over more area, and an exit pupil so small that floaters in your own eye start to show. On most nights the atmosphere caps things lower still, around 200×, whatever the instrument.

  • It will look like the picture on the box.

    The human eye has almost no colour response at low light levels, so nebulae and galaxies appear grey — sometimes faintly green. The photographs are long exposures, often in false colour, often from space. What you actually see is a faint grey shape, and it is genuinely thrilling, because those photons left their source before there were people.

  • Buy the biggest you can afford and grow into it.

    The best telescope is the one that gets carried outside. A 200 mm that needs two trips and lives behind the lawnmower is used four times a year; a 130 mm by the back door is used forty. Aperture only counts when it is pointed at the sky.

All of them →