Two eyes, a wide field, and no setup at all
A pair of binoculars is the instrument most often recommended before a first telescope and most often abandoned afterwards, which is a shame, because the wide field and the use of both eyes show sweeps of the Milky Way that no telescope frames. The two numbers in the name are the magnification and the aperture in millimeters, and dividing the second by the first gives the exit pupil — the width of the cone of light leaving the eyepiece. If that cone is wider than the pupil of the observer, the surplus light is thrown away — and since a dark-adapted pupil measures around 7 mm (0.28 in) in a young adult but commonly 5 to 6 mm (0.20 to 0.24 in) by about fifty, the same binoculars deliver differently to two people standing side by side. That 7 mm (0.28 in) figure is exactly why the 7×50 became the classic night glass: 50 divided by 7 is a hair over seven. The true field of view, given in degrees, tells you what actually fits; it is not the apparent field printed in some listings. Prism glass separates the shelf more than most buyers expect: BAK-4 prisms deliver a round exit pupil where BAK-7 prisms cut the edges into a square. Above roughly ten times magnification, a hand-held image trembles enough to hide what the aperture collected, so read the tripod thread as a specification and not an extra. Eye relief decides whether spectacles can stay on. We compare aperture, magnification, exit pupil, true field of view, prism type and coatings, eye relief, close focus, weight, tripod mounting and supplied accessories.
10x · 50 mm (1.97 in) · BK-7 porro prisms · fully coated · InstaFocus
A long-running 10x50 porro binocular from Bushnell's Falcon line, with BK-7 prisms, fully coated optics and a central InstaFocus lever, and no waterproofing claimed.
Best for: A first, inexpensive pair kept in the car for whatever the sky or the day offers
≈ $41
12x · 50 mm (1.97 in) · 18 mm prisms · 4.2 mm (0.17 in) exit pupil
A budget 12x50 binocular with 18 mm prisms and 50 mm objectives, supplied with a carrying case, neck strap and cleaning cloth.
Best for: Daytime distance viewing, with astronomy from a braced or seated position
≈ $69
10x · 50 mm (1.97 in) · porro prisms · multilayer-coated · long eye relief
Nikon's Action 10x50: a rubber-armored porro binocular with multilayer-coated lenses, turn-and-slide eyecups, long eye relief for glasses and a tripod-ready body.
Best for: Sweeping the Milky Way and open clusters, on a tripod or from a reclining chair
≈ $130
10x · 50 mm (1.97 in) · porro prisms · multi-coated · TP-3 tripod adapter optional
A 10x50 porro binocular from Pentax's Jupiter series, with multi-coated optics, a rubber-coated body and an optional TP-3 tripod adapter.
Best for: A first serious binocular for the sky, with a tripod adapter available when the arms tire
≈ $99
10x · 50 mm (1.97 in) · 282 ft field at 1000 yd · BaK-4, silvered prisms · 26.1 oz (740 g)
A waterproof, nitrogen-filled 10x50 with BaK-4 prisms carrying an extra silver coating, published with its field of view, close focus, dimensions and weight.
Best for: The observer who wants to compare figures rather than adjectives before buying
≈ $226
10x · 50 mm (1.97 in) · BaK-4 prisms · waterproof, gas-filled · 758 g (26.7 oz)
A waterproof, gas-filled 10x50 porro binocular with BaK-4 prisms, full multi-coating, a UR prism coating, twist-up eyecups and a metal center focus, published with its weight and size.
Best for: Dusk and night-sky use in damp or cold weather that would fog an unsealed pair
≈ $166
The aperture of each objective decides what is collected. On astronomy binoculars it is the most important figure.
True field of view decides how much sky is visible at once, and that is what binoculars do better than a telescope.
Weight decides how long an observation really lasts. Past a certain threshold, a tripod becomes compulsory.
The diameter of the beam leaving the eyepiece, that is the aperture divided by the magnification. It is published and compared against the eye’s pupil.
It narrows the field and amplifies shake. Magnification is published as a figure, not as a quality.
The portion of sky visible, in degrees or in meters at a thousand meters. It is published on every entry.
It explains the shape of the body and part of the light transmission. It is published alongside the coatings.
A great deal for spectacle wearers. The published figure says whether the whole field stays reachable with lenses on.
Published weight and magnification decide that together. Many astronomy binoculars are designed for a support.
It concerns terrestrial use more than the sky. It is published because these binoculars often serve both.
Binoculars give a wide field and are picked up instantly. This site publishes the figures for both families.
Astronomy binoculars come down to three linked numbers: the aperture that gathers, the magnification that narrows the field, and the exit pupil that says what the eye actually receives.
The column is shown only when four instruments in five publish the figure. Below that, it would be comparing the absence of numbers.
| Model | Price | Exit pupil | Magnification | Prism type and coatings |
|---|---|---|---|---|
| Bushnell Falcon 10x50 (13-3450C) | $41 | 5 mm (0.20 in) at 10x, the quotient of the published figures | 10x in the title and the description · one bullet of the same listing says 12x, which contradicts the model name | BK-7 porro prisms · fully coated optics (not multi-coated) · no waterproofing or gas filling claimed |
| occer 12x50 | $69 | 4.2 mm (0.17 in), the quotient of the two published figures | 12x | 18 mm prisms, stated · prism glass and coatings not published |
| Pentax Jupiter 10x50 (65912) | $99 | 5 mm (0.20 in), the quotient of the two published figures | 10x | Porro prisms · multi-coated optical elements to reduce reflections |
| Nikon Action 10x50 | $130 | 5 mm (0.20 in), the quotient of the two published figures | 10x | Porro prisms · multilayer-coated lenses |
| Bresser Wave 10x50 (1331050) | $166 | 5 mm (0.20 in), the quotient of the two published figures | 10x | BaK-4 glass · fully multi-coated optics · UR coating on the prisms · protective gas filling against fogging · waterproof |
| Eschenbach Arena D+ 10x50 | $226 | 5 mm (0.20 in), the quotient of the two published figures | 10x | BaK-4 prisms with an additional silver coating, stated to raise reflectivity by 4% · fully multi-coated lenses · nitrogen-filled and waterproof |
Specifications: manufacturer sheets for telescopes and observing optics and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: November 7, 2026.
Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.
