Astronomy asks different things of a pair of binoculars than daylight use does, and the specification that matters most, exit pupil, is the one almost no listing prints. This page is how to read a pair for night use.
Exit pupil, and why it decides
Divide the objective diameter by the magnification. A 10x50 gives five millimetres, a 7x50 gives just over seven, a 10x25 gives 2.5. A dark adapted adult eye opens to between five and seven millimetres, falling with age. An exit pupil larger than your pupil wastes light at the edges; one much smaller gives a dim image regardless of the aperture.
Field of view, and what fits in it
A typical 10x50 shows about six degrees, which is twelve full moons across. That is enough to frame the Pleiades comfortably, to sweep the Milky Way, and to find things without a chart. Wide angle designs push toward seven or eight degrees and are worth the premium for sweeping.
Coatings and prism glass
Fully multicoated is the phrase to look for, meaning every air to glass surface is coated. BAK4 prism glass rather than BK7 gives round rather than squared off exit pupils and better edge illumination. Both are printed on most specifications and both are cheap ways to tell serious pairs from decorative ones.
Questions people ask about binoculars
What are the best binoculars for astronomy?
Ten by fifty handheld, or 15x70 on a tripod for more reach. Fully multicoated optics and BAK4 prisms are the specification markers worth checking.
What magnification is best for astronomy binoculars?
Seven to ten times handheld. Higher magnifications need mounting, and mounted 15x70 or 20x80 pairs are a well established niche.
Can you see galaxies with binoculars?
The brightest ones, yes: Andromeda is easy, and several others are visible from a dark site as faint smudges. Detail needs a telescope.