Binoculars: compact binoculars, big binoculars and what binocular numbers mean

Printed prices, verified

Reading a pair of binoculars from its numbers

1. The first number is magnification. Seven times, ten times, fifteen times. Above about ten, a handheld view starts to shake enough that detail is lost, which is why 7x50 and 10x50 have been the night sky standards for decades.
2. The second number is aperture. In millimetres, per side. A 10x50 gathers about the same light as a 50mm telescope, which is why a cheap pair shows the moons of Jupiter and a pocket pair does not.
3. Divide them for the exit pupil. Fifty divided by ten is a five millimetre exit pupil, which suits most adult eyes at night. A 20x50 gives 2.5mm, which is dim, and a 7x50 gives just over seven, which is more than an older eye can use.
4. Then pick them up. Weight and the fit of the eyecups matter more than any specification once you are past the numbers, and neither shows in a listing.

Why this index prices no binoculars

Two of the eight brands here keep a live binocular page and neither publishes a price this index can read; the binocular specialists that would fill the column, Vortex, Athlon, Opticron, Svbony and Orion, serve pages that carry no readable price text at all. A comparison table with two occupants is a thin page pretending to be a comparison, so the category has answer pages and no price ranking.

That is a limitation of this site rather than of the market, and it is recorded here so nobody reads its absence as a judgement about binoculars.

Where binoculars beat a telescope outright

Anything large and faint. The Pleiades, the Hyades, the Andromeda galaxy, the sweep of the Milky Way through Cygnus and the big open clusters all fit in a binocular field and none of them fits in a telescope's. Two eyes also see more faint detail than one, which is a real and measurable effect rather than folklore.

They also win on the thing that decides how much anyone observes, which is friction. A pair of binoculars by the door gets used on a clear evening that would never have justified carrying a telescope outside.

Common questions

What do the numbers on binoculars mean?

Magnification times aperture in millimetres. A 10x42 magnifies ten times through 42mm objectives; a 7x50 magnifies seven times through 50mm and gathers more light.

What size binoculars are best for stargazing?

Ten by fifty is the usual answer, because it is the largest aperture most people can hold steady. Anything above about 15x needs a tripod, and above 70mm the weight decides it for you.

Are compact binoculars any good at night?

For the night sky, not really. An 8x25 gathers a quarter of the light of an 8x50, and the small exit pupil makes the view dim. They are excellent for daylight and for carrying.

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