10x50 porro prism binoculars, green

A size that has lasted

Porro prism binoculars have the familiar stepped shape: the objective lenses sit further apart than the eyepieces, because the light is folded sideways through two prisms. The 10x50 has been one of the most common sizes for decades, and NASA lists 10x50 as the top end of the range it suggests for a first pair for stargazing.

The 50 mm lenses give a 5 mm exit pupil. That is larger than your pupil in daylight and close to it at dusk, so the view stays bright as the light fades. It also suits coastal walks, where ships, seabirds and headlands are often far away.

What the supplier lists

This model is part of a series that the supplier also offers as a 20x50. For the series the supplier lists BaK-4 porro prisms, a multi-coated green lens coating, a centre focusing wheel with dioptre adjustment on the right eyepiece, a body of 190 x 180 x 65 mm and a weight of about 750 g. The body is covered in rubber armour. The supplier gives no waterproof rating, so treat it as a pair for dry and showery weather.

We chose the 10x version on purpose. At 20x the exit pupil shrinks to 2.5 mm and hand shake becomes hard to live with. At 10x most people can hold the view steady, and a tripod is optional rather than essential.

Using it at night

Let your eyes adapt to the dark for 20 minutes or so, sit in a garden chair and rest your elbows on the armrests. The Moon, the Pleiades and the band of the Milky Way on a dark night are good first targets. Binoculars for stargazing has a full list and tips on steadying the view. Never look at the Sun through binoculars.