Posts Tagged ‘astronomy’

Choosing Binocular Astronomy – Part 8 & Final

Monday, September 7th, 2009

(This is the final installment of this terrific article. Many thanks again to Ed Ting for permission to serialize his article here. I think it’s mandatory reading for anyone who is considering telescope binoculars for astronomy viewing. Ted)

Keep It Simple

Let me offer one final caution: Keep it simple. As a rule you should avoid zoom binoculars, at least for astronomical use. Good zoom eyepieces require a very high (and expensive) standard of precision manufacture that’s usually not met.

Likewise, binoculars with built-in cameras may be okay for casual daytime use, but not at night. They’re gimmicky toys.

Most binoculars have center focus, meaning that you focus both barrels at once by turning a knob or a rocker in the center. This is great for when the distance of your target often changes, such as in birdwatching, or when you often pass the binoculars back and forth between people. But the night sky always stays at infinity focus, and you’re probably observing it alone. So eyepieces will do just fime. This not only saves you money but provides better mechanical stability and gets rid of a common cause of eyepiece misalignment (slight tipping of the center-focus mechanism).

But no matter what imperfections you have to live with (and face it, optical perfection does not exist), you’ll find that binoculars can show you more of the universe than you probably imagined.

(Note:  I want to thank Ed Ting again for his permission in reprinting this thorough primer on starting with Binocular Astronomy. Based in Amherst, New Hampshire, Ed Ting reviews stargazing equipment for his website, www.scopereviews.com.  This article appeared previously in Sky and Telescope.com.

For a great selection of telescope binoculars for astronomy viewing, please visit our site and check out our astronomy binoculars Ted)

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Choosing Binocular Astronomy – Part 7

Thursday, August 20th, 2009

(Thanks to Ed Ting for permission to serialize his article here. I think it’s mandatory reading for anyone who is considering telescope binoculars for astronomy viewing. Ted)

Testing Under the Stars

If and when you do get a chance to test binoculars under the stars, take it.  A star at night is the most stringent indicator of optical quality. You may even find a daytime “artificial star” such as sunlight glinting off a distant insulator on a power pole or a distant piece of shiny metal.

Center it in the field of view. Looking with one eye at a time, can you bring it to a perfect point focus? Or, as you turn the knob, do tiny rays start growing in one direction before they have shrunk all the way in the direction at right angles? This astigmatism is especially bothersome when viewing stars. If you have astigmatism in your eyes, be sure to wear your glasses when doing this test.

If, as you turn the focus, little rays start growing out of the star in all directions before the rest of the star comes down to focus, you’re looking at spherical aberration. This problem too may be in your own eye, even if you’re wearing your glasses. If it is, all binoculars with a given size exit pupil will show the same problem. To reduce it, choose higher-power binoculars; these yield a smaller exit pupil for a given aperture. Unfortunately, your eye’s spherical aberration cannot be corrected with glasses.

Now move the star from the center of the field to the edge. It will go out of focus unless you have a perfectly flat field and freedom from various other aberrations. As a rule of thumb, no degradation should be visible until the star is at least halfway to the edge of the field.

All our Barska telescope binoculars and astronomy binoculars have limited lifetime warranties from defects.

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Choosing Binocular Astronomy – Part 4

Monday, July 27th, 2009

(Thanks to Ed Ting for permission to serialize his article here. I think it’s mandatory reading for anyone who is considering telescope binoculars for astronomy viewing. Ted)

Another recent innovation is image-stabilized binoculars. These employ the same ingenious mechanisms found inside the best video cameras. Push a button and the shaky magnified view suddenly calms down, almost freezing in place. The result is that you can use higher magnifications, get away with slightly less aperture, and yet still see more than with conventional binoculars.

Image-stabilized binoculars

Image-stabilized binoculars. Push the button on top, and the view holds miraculously still. Image-stabilized units are, however, expensive and a bit bulky, and they eat batteries.
Night Sky: Craig Michael Utter

I was skeptical when these little marvels were introduced, but I was quickly won over. When I first used Canon’s compact little 10×30 image-stabilized binoculars (shown at left) from a dark-sky site, I had no trouble picking out the galaxies M81 and M82 near the Big Dipper. In fact, I actually tried to jiggle the view, but it refused to budge!

You may be thinking that more magnification is better, but in practice once you get to 10x and above, it gets harder (and more tiring) to hold binoculars steady if they’re not on a mount or equipped with image stabilization.

There’s some debate on what magnification is best. Low-power advocates recommend staying with 7x or 8x, whereas the high-power types say that the increased detail and darker sky background provided by 10x units are worth the narrower field of view and extra jiggling.

My take on this? I’m in the low-power camp. I don’t find the visual difference between 7x and 10x all that great, but I’m noticeably less fatigued when using low-power glasses. If you get the chance, give both a good try and see which you prefer.

Looking at the exit pupils

The exit pupils are the little disks of light you see floating behind the eyepieces.
Night Sky: Craig Michael Utter

A related consideration is the exit pupil, the size of the little round disk of light that you see floating in the air behind the eyepieces when you hold the binoculars out in front of you toward a bright sky or a bright indoor wall. The size of the exit pupil is an important factor that’s often overlooked. To determine it, just divide the aperture by the magnification — and luckily these are inscribed right there on the back facing you. For example, 7×50 binoculars have about a 7-mm exit pupil, while 10×50s have a 5-mm exit pupil.

Why is this important? Because the bright disk of the exit pupil should fit inside the pupil of your eye. And not everyone’s eyes open to the same diameter in the dark. Young people (under age 30 or so) have pupils that open to about 7 millimeters across. While individuals vary a lot, the rule of thumb is that after age 30 you lose 1 mm of exit pupil every 10 or 15 years. So older eyes can’t take advantage of binoculars with large exit pupils and, as a result, might see no difference between 7×35s and 7×50s. The extra light collected by the bigger 7×50s isn’t fitting into your eyes; it’s just going to waste. Score a big point for the high-power camp, at least if you’re getting on in years; the higher the power, the smaller the exit pupil.

(Note:  Our large Barska astronomy binoculars, like all of our telescope binoculars for astronomy, when used with a tripod or stabilized in another way, will give you the closest experience to a telescope you can get, with top quality optics.  Ted)

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Choosing Binocular Astronomy – Part 3

Sunday, July 26th, 2009

(Thanks to Ed Ting for permission to serialize his article here. I think it’s mandatory reading for anyone who is considering telescope binoculars for astronomy viewing. Ted)

Buying Binoculars for Stargazing

If you don’t already have astronomy binoculars (or if you’re outgrowing the ones you’ve got), it’s time to buy. But there are so many choices. Are some better for astronomy, as opposed to birdwatching or baseball games? You bet!

Astronomy is done in the dark, so you really want big aperture: big front lenses. These collect lots of light so you can see fainter things. This doesn’t matter so much in the daytime, when there’s plenty of light and you can get by with small front lenses — allowing daytime binoculars to be smaller, lighter, and less expensive.  But for astronomy, the bigger the aperture the better.

Porro-prism binoculars

Binoculars come in two basic styles: the step-sided Porro-prism design here, and the H-shaped roof-prism design shown below. Porro-prism instruments are less expensive and excellent for astronomy.
Night Sky: Chuck Baker

You also want high optical quality. Stars and faint celestial objects seen against a dark sky are much more demanding than daytime scenes, so mediocre optics display their flaws much more obviously when you’re observing the night sky rather than eatching the pitcher’s mound. In general, price is a pretty good indicator of optical quality. The best optics are not going to be cheap.

Binoculars come in two body styles: the familiar “stepped” look of the Porro-prism design (right), and the sleeker “H” profile of the roof-prism design (below right). Most binoculars marketed for astronomy use Porro prisms, named for the Italian optician who invented them in the 1850s.

Roof-prism binoculars

Roof-prism binoculars are a good choice when lightness and compactness matter more than high cost. Beware of cheap versions (and ultra-cheap fakes).
Night Sky: Chuck Baker

Roof-prism units are smaller and lighter-weight but have a more complicated, touchy optical design, which makes them more difficult and expensive to manufacture well. As a result, roof-prism binoculars tend to cluster at the high end of the market and, inexplicably, at the bottom end too — but not so often in between. A saying around my local astronomy club is that if your roof-prism binoculars don’t seem to be performing well, you didn’t spend enough money!

In recent years there’s been a new twist on the bigger-is-better theme: giant telescope binoculars. These are impressive, even imposing-looking devices. It’s as if someone put your friendly 7×50s on steroids. Common apertures include 70, 80, and even 100 mm. (Fujinon even makes a 150-mm model — the equivalent of two 6-inch telescopes, one for each eye!) For such beasts a tripod, preferably with a special binocular mount that allows you to aim upward, is mandatory. While they’re a good supplement to your gear collection, I don’t recommend giant binoculars as your primary instruments — they’re just too unwieldy. Get more modest 7×40s or 10×50s first, and consider buying these big shots later.

(Note:  This decision rests on how you use the binoculars – if you will use your car to get where you want to stargaze – go for the big ones.  If you want them for camping – go for more compact – but not less than a 50MM objective lens.  And never, never compromise on quality – like our Barska binoculars with their lifetime warranty. Ted)

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