how to... choose the right binoc­u­lars

All About Space - - Contents -

How to pick the right pair for clear, crisp views

With Christ­mas around the cor­ner, no doubt many of you will be won­der­ing what to buy that spe­cial some­one. If they are in­ter­ested in as­tron­omy the ob­vi­ous gift would be a tele­scope, right? Wrong! They might not be ready for some­thing as pow­er­ful and as com­pli­cated as that, es­pe­cially if just start­ing out in the hobby. A great al­ter­na­tive is a pair of binoc­u­lars – they’re not so pow­er­ful that they can’t be used by an ab­so­lute be­gin­ner, and they’re cheaper and less com­pli­cated to use than a tele­scope too. But which pair to buy?

The good news is that it is really easy to iden­tify a pair of binoc­u­lars that will be suit­able for as­tron­omy use; all you have to do is hold them, take a look at and through them and work out a very sim­ple sum us­ing the num­bers printed on them.

First of all, weight is very im­por­tant. If a pair of binoc­u­lars is too large and heavy for them to be held and sup­ported by hand they will quickly be­come a chore to use. If you can’t sup­port them prop­erly ev­ery­thing you look at through them will shud­der and shake. You can mount larger pairs of binoc­u­lars on a tri­pod with an adap­tor, but that makes it harder to aim them at their tar­gets. Avoid that for an ab­so­lute be­gin­ner. On the other hand, a pair of binoc­u­lars that is very small and light­weight will of­fer poor mag­ni­fi­ca­tion and a very nar­row field of view, so be­ware those too.

There’s no sub­sti­tute for ac­tu­ally look­ing through a pair of binoc­u­lars, and a good re­tailer will have no prob­lem with you tak­ing your prospec­tive pur­chase to their shop door and try­ing them out. If the image you see af­ter fo­cus­ing is still blurry, has colour fringes or is even split into two parts, that pair is no use. Look at the colours of the front lenses too. Ones that are coated or­ange, red or green are de­signed to cut down con­trast – use­ful for day­time ac­tiv­i­ties, but not for as­tron­omy be­cause you want as much con­trast as pos­si­ble.

Ev­ery pair of binoc­u­lars has two num­bers on it – 7x35, 10x50, 25x50 and so on. These stand for the power of mag­ni­fi­ca­tion and the aper­ture of their front lenses. To be good for as­tron­omy the sec­ond num­ber di­vided by the first should give you a value of five or higher. This fig­ure rep­re­sents how much light comes out of the binoc­u­lars and goes into your eyes. A fig­ure of five is ideal.

Don't panicIt’s not as hard to pick a good pair of binoc­u­lars as you might think. It just takes a lit­tle time and com­par­i­son. You get what you pay forDon’t be tempted by bud­get or cheap binoc­u­lars. It’s well worth pay­ing a lit­tle ex­tra for equip­ment that will last. Don't be afraid to askA good re­tailer won’t mind you ask­ing if you can test out­side their shop if it helps you buy the right equip­ment. Crunch the num­bersDo­ing a sim­ple sum will save you buy­ing the wrong binoc­u­lars; don’t just as­sume the pair you like the look of will work.Avoid shake, rat­tle and rollIf you feel you need to put your binoc­u­lars on a tri­pod, go ahead. If your hands are shak­ing you won’t be able to see a thing through them.

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