A pair of 10x50s from the jetty: what binoculars really reach

Why the binoculars go out more often

The reflector is a twenty-minute commitment before the first proper look: carry it out, let it cool, find the finder, wonder about collimation. The binoculars are a decision I can make in thirty seconds while the kettle boils. Over four years that difference has decided almost everything, because the clear gaps in an archipelago autumn are rarely three hours long. They are twenty minutes between two banks of cloud, and the instrument already hanging round my neck is the one that sees anything at all on a night like that.

There is also the matter of field. Ten by fifty gives me somewhere around six degrees, enough to hold the whole of the Pleiades with space around them, to sweep a constellation rather than interrogate a coordinate, and to find things by star-hopping without ever losing the pattern. Two eyes are more comfortable than one for long looks, and the image comes the right way up, which matters more than purists tend to admit when you are trying to match what you see against a chart by red torchlight.

The autumn list that works from here

From late September the sky finally gets dark again, and the objects that suit this instrument are mostly overhead, where the city glow is weakest. The Andromeda galaxy passes close to the zenith here in autumn, which is one genuine advantage of the latitude. It shows as an obvious oval smudge in binoculars, considerably larger than most people expect, with a brighter core and a soft extension running off to one side. The Double Cluster in Perseus is the other reliable target, two knots of resolved stars sharing a single field.

The Milky Way through Cassiopeia and Cygnus repays slow sweeping on a good night, though from here it is a grainy band rather than the structured river you get further south and further from a city. Later in the evening the Pleiades clear the trees, and by December the Auriga and Gemini stretch is high enough to be worth an hour. I keep the list short and revisit the same dozen objects, because knowing what something looked like last November is how you notice that tonight is unusually transparent.

• Andromeda galaxy: near the zenith in autumn, obvious, bigger than expected
• Double Cluster: two resolved knots in one field, best near midnight in October
• Pleiades: the whole group with room to spare at six degrees of field
• Milky Way through Cassiopeia: grainy here, not spectacular, still worth sweeping
• Crescent moon: earthshine is easiest of all in a small instrument

Holding them still

Hand-held ten-power sits at the edge of what most people can hold steadily, and the difference between braced and unbraced is roughly a magnitude of faint detail. I learned this properly in a deck chair. Leaning back with my head supported took the arms out of the equation entirely, and objects that had been a suspicion became plain the moment my elbows stopped working. A gatepost, a doorframe or the corner of a boathouse will do much the same job for anything that is not directly overhead.

The fifteen by seventies, which look like the obvious upgrade, are not hand-holdable at all, and mine spent a year in a cupboard before I accepted that they need a tripod and some way of looking upwards without kneeling in wet grass. A parallelogram arm solves that elegantly and costs more than I wanted to spend, so I use a photo tripod with the legs splayed wide and accept that anything above sixty degrees means lying flat on the jetty. That is less absurd than it sounds, and warmer with a mat.

What binoculars will not do

Binoculars will not show a planet as anything other than a disc, and at ten power Jupiter is a small bright dot with four points strung out beside it, which is genuinely moving the first time and not much of a view the second. Detail on Mars is out of the question at any useful distance. The rings of Saturn do not resolve; at best the planet looks slightly oval and wrong, which is roughly where Galileo left it. For any of that you need magnification, and therefore a mount that holds still.

They are also unforgiving about light. Under the western part of my sky, where the city dome sits, a fifty-millimetre aperture simply cannot pull a faint diffuse object out of a bright background, and no amount of averted vision changes the arithmetic. The honest summary is that binoculars here are excellent for objects that are large, bright and high, and useless for anything small, faint and low. Knowing which is which before going outside saves a great deal of standing in the cold being disappointed.