Binoculars - What should I look for?

I have mentioned binoculars many times throughout these posts and I thought it would be good to discuss them more.  An introduction to telescopes was provided last month.

Telescopes - What should I look for?

I can not stress enough, binoculars are amazing for astronomy.  A telescope is not necessary to observe a lot of really amazing things in the night sky.  Binoculars are relatively cheap and very portable.  A lot of people already own a pair of binoculars and there is nothing required to adapt them for celestial viewing.  Even with the smallest 7x35 you can increase the number of stars you see by 30.

The first thing to understand about binoculars is its magnification and aperture.  Most binoculars are marketed as 7x35, 10x50 etc.  The first number represents the magnification and the second number is the aperture in millimeters.  As with telescopes, the larger the aperature, the more light you will be able to gather.  This is helpful for finding dim objects.  Also note that the higher the magnification, the higher your hand shakes are magnified, so you will want to look into tripods or mounts.

The field of view is also an important factor when purchasing a set of binoculars.  Typical binoculars can range anywhere between 3° and 8°.  Consider the target you would like to look at to determine how wide you want your field of view.  Most deep-sky objects are under 2° so you should have no trouble.  However, some common asterisms can be much wider and low power binoculars should be used.

There are many publications that can be found at your local library specifically for binocular astronomy.  Most astronomy magazine publications have a monthly article dedicated to the many wonders you can see with binoculars.  A telescope's narrow field of view can be a detriment in many cases.  You can purchase quality wide-field eyepieces for your telescope to see wider views but they can sometimes run you up $1000 a piece.

Another thing to consider is image-stablised binoculars.  You can look through your binoculars and then press a button and everything becomes still.  These are amazing.  However, these are also expensive and will chew through your wallet and batteries.  If you really want to try them out I would recommend attending an observing party or astronomy open house.

Let's talk about small binoculars (<50mm aperture)

They are very portable and can fit in your glove compartment, handbag or a small luggage compartment in your suitcase.  These are excellent to start out in astronomy and they usually have a very wide field of view.   This makes it exceptionally easy to hop from star to star in your favourite constellation.  They are also quite useful for learning the sky around a telescopic target that you might try to search for later in the evening.

7x35 Binoculars

Medium binoculars (50-100mm aperture)

I have a 15x70 set that I use every night it is clear.  With medium binoculars you are bordering on stability issues.  They may get heavy after awhile and you find yourself trembling.  You can remedy this by lying on your back and resting them against your eyes or gripping them closer to the objective lens.  Most medium binoculars can also be attached to a tripod but, of course, forces you to carry a tripod around with you.  The field of view is typically narrower so more sky experience is necessary for finding a specific target.  That being said, I've found many star clusters and nebulae with my binoculars and their sharp focus is amazing.  You can pick out individual craters and maria on the Moon and even see moons of the Jovian planets.  My set are shown below.

15x70 Binoculars (4.4° Field of View)

Large binoculars (>100mm aperature)

Stability and portability are major drawbacks of large binoculars.  You will almost definitely have to get a tripod or mount to attach your binoculars.  A 100mm set is like lifting two 4" telescopes to your eyes every time you want to see something.  The field of view is relatively narrow and closes off certain asterisms that pop out with a smaller set.  However, deep-sky objects are absolutely amazing and clusters are well defined.  Tight double stars are easily separated, cloud bands on Jupiter pop into view and you can even see the rings of Saturn.  Taking a pair of these (with a mount) to a dark site would be amazing.  I've seen some sets that are bordering on 50lbs, those would be fun to look through.

100mm Binoculars

You can even get carried away and build an observatory around binoculars as in Arizona.

Large Binocular Telescope