Binoc­u­lars for Christ­mas

Penticton Herald - - OPINION - KEN TAP­PING

Ev­ery astronomer, young or old, be­gin­ner or ex­pe­ri­enced, should have a good pair of binoc­u­lars, maybe more than one. They can be used for a short bit of observing, or a ses­sion of se­ri­ous as­tro­nom­i­cal study. These are the best tools for search­ing for comets, ex­plor­ing the Milky Way, or just tour­ing the sky.

A pair of binoc­u­lars con­sists of two tele­scopes fixed to­gether. Mag­ni­fi­ca­tions are gen­er­ally fairly low, typ­i­cally be­tween seven and 10, al­though some of­fer a higher power. From an as­tro­nom­i­cal point of view their main func­tion is to col­lect lots of light.

For ex­am­ple, binoc­u­lars with ob­jec­tive lenses with a di­am­e­ter of 50 mil­lime­tres will col­lect about 100 times as much light as our dark- adapted eyes.

They will re­veal the struc­ture of the Milky Way, the bright clouds where new stars are be­ing born, the four bright­est moons of Jupiter and how they change po­si­tions from night to night, and many other things that would other­wise be too faint to see.

Binoc­u­lars are de­scribed by two num­bers, sep­a­rated by an “x.” For ex­am­ple 8x30, 7x50, 10x50, 12x75 and so on. When dis­cussing them, we pro­nounce the “x” as “times,” as in “10 times 50.”

The first num­ber is the mag­ni­fi­ca­tion, and the sec­ond is the di­am­e­ter of the ob­jec­tive lens in mil­lime­tres. The ob­jec­tives are the big lenses at the front of the binoc­u­lars. They ful­fil two func­tions: they col­lect the light and form an im­age out of it. We then view that im­age with the smaller, eye­piece lenses at the back end of the binoc­u­lars.

How­ever, from a prac­ti­cal point of view there is a limit to the size of the ob­jec­tives and how much mag­ni­fi­ca­tion we should have. Binoc­u­lars with ob­jec­tives big­ger than about 50 mm are too heavy for the av­er­age observer. Those with ob­jec­tives big­ger than about 75 mm will def­i­nitely need a tri­pod.

Mag­ni­fi­ca­tion is an is­sue too. In ad­di­tion to mak­ing things look larger, the field of view is smaller, mean­ing it gets hard to find or fol­low things, and any shak­i­ness of your hands gets mag­ni­fied too. Some sort of sup­port helps.

This prob­lem has been solved with the in­ven­tion of binoc­u­lars with “im­age sta­bi­liza­tion.” Sen­sors, mov­able mir­rors or prisms and some clever elec­tron­ics sense the shak­ing of the binoc­u­lars and cor­rect the im­age so that it does not move. These in­stru­ments are still ex­pen­sive and most have rather small ob­jec­tive lenses, but they are im­prov­ing rapidly and fall­ing in price.

At the mo­ment, for less than the price of im­age-sta­bi­lized binoc­u­lars you can buy a re­ally high-qual­ity pair of the stan­dard kind.

It pays to try binoc­u­lars be­fore you buy them. A prob­lem with less ex­pen­sive ones is that the two tele­scopes are of­ten not point­ing in ex­actly the same di­rec­tion. If this prob­lem is bad, you will no­tice it im­me­di­ately when you try to use them. If it is less se­ri­ous your brain will cor­rect it, pro­duc­ing a slight feel­ing of dis­ori­en­ta­tion and even­tu­ally a bad headache.

No mat­ter what the sales­per­son says, it should be pos­si­ble to ad­just the binoc­u­lars to make them com­fort­able to use. If he or she does not know how to help you, shop else­where. If you can­not get ut­terly com­fort­able, don’t buy them.

These is­sues might sound scary to a be­gin­ner or non-astronomer. How­ever, the so­lu­tion is sim­ple: seek ad­vice. If you have a sci­ence store nearby, go there. If there isn’t one, con­tact the lo­cal cen­tre of the Royal As­tro­nom­i­cal So­ci­ety of Canada. The RASC has many ama­teur as­tronomers who can give re­ally good ad­vice on what to get and where to get it.

You could buy the fam­ily astronomer a mem­ber­ship while you’re at it. You’ll lo­cate your near­est cen­tre by hav­ing a look at https://www.rasc.ca/lo­ca­tion­sacross-Canada.

Mars lies low in the south af­ter sun­set and Venus shines low in the south­east be­fore dawn. Mer­cury is there too, lurk­ing low in the dawn twi­light. The Moon will reach First Quar­ter on the 15th.

Ken Tap­ping is an astronomer with the Na­tional Re­search Coun­cil's Do­min­ion Ra­dio Astro­phys­i­cal Ob­ser­va­tory, Pen­tic­ton.

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