EQUIPMENT REVIEW Sometimes, observing is best with both eyes open. /// BY PHIL HARRINGTON under $100

The diameter of the can be Maybe you’re new to the astronomy calculated by dividing the - hobby and thinking about buying a . More often than diameter by the . Thus, in not, your best first purchase isn’t a telescope, but binoculars. the case of 7x50 binoculars, the exit pupil will measure 7.1mm across. Getting used to the narrow, flipped-around images through a Traditionalists may argue binoculars telescope can be daunting. Binoculars are more natural, almost with 7mm exit pupils are the best for like extensions of our eyes. Every amateur astronomer — night viewing. That notion probably dates back to World War II, when the indeed every person — should own number is the magnification, and the U.S. military issued 7x50 “night .” binoculars. second is the diameter of the front Today, however, most of us view Of course, that begs the question: (objective) in millimeters. Light through light-polluted skies under which “Which binoculars?” There are many fac- passes through each objective lens, our pupils never dilate fully. Further- tors to take into account, but the answer reflects through a assembly, and more, as we age, our pupils don’t dilate often boils down to budget. It probably then exits through an in the to the degree they did when we were makes sense to spend as little as possible form of a magnified cylinder of light younger, regardless of darkness. to fuel a budding interest. called the exit pupil. As a result, many observers prefer But just as the marketplace is flooded Ideally, the exit pupil should match 10x50 binoculars because of their 5mm with low-price , it is also belea- the diameter of your eyes’ pupils. If the exit pupils. Also, the slightly higher mag- guered with economy binoculars. You binoculars’ exit pupils are larger than an nification produces better image contrast can find dozens out there. Which one is observer’s pupils, light will be wasted. (the bright-to-dark ratio) than through a

best? Decisions, decisions … If, on the other hand, the binoculars’ 7x50, and the 10x50 model is still light ZUBACK : WILLIAM exit pupil is too small, the view will be a enough to support by hand.

The numbers game circle surrounded by a black ring. Fully Some observers prefer larger binocu- ASTRONOMY All binoculars are specified by two num- dilated, the eye’s pupil expands to 7mm, lars because they offer increased light-

bers, such as 7x50 or 10x70. The first but this varies from person to person. gathering power. The increased size and IMAGES ALL

Orion Scenix Bushnell Legacy Eagle Triumph

© 2009 Kalmbach Publishing Co. This material may not be reproduced in any form without permission from the publisher. www.Astronomy.com /// FIND THE RIGHT BINOCULARS FOR YOU

Model Price Magnif. Exit pupil Eye relief Weight Coatings (x) (mm) (°) (mm) (mm) (ounces)

Bushnell Legacy $99 10 50 7.2 5.0 9 28 BaK-4 MC OptiView LPR $100 10 50 7.0 5.0 13 32 BK-7 FC Celestron SkyMaster $88 15 70 4.4 4.7 18 48 BaK-4 MC Celestron UpClose $37 10 50 7.0 5.0 11 25 BK-7 FC Eagle Optics Triumph $99 10 50 6.5 5.0 19 30 BK-7 FC Action $100 10 50 6.5 5.0 12 34 BaK-4 MC Oberwerk 8x56 $100 8 56 6.0 7.0 24 32 BaK-4 FMC Oberwerk 11x56 $100 11 56 4.0 5.1 19 32 BaK-4 FMC Orion Scenix $90 10 50 7.0 5.0 12 28 BaK-4 FC Orion WorldView $40 10 50 6.5 5.0 14 29 BK-7 FC XCF $90 10 50 6.5 5.0 13 31 BaK-4 MC Swift Aerolite $81 10 50 5.2 5.0 13 37 BK-7 FC Sonoma $60 10 50 6.5 5.0 9 23 BK-7 MC

Coatings: FC: Fully coated optics MC: Multicoated optics FMC: Fully multicoated optics

weight, however, is difficult to support by hand — especially for extended lengths of time — and requires a tripod.

Maximizing light throughput When evaluating binoculars, it’s also important to consider glass and coatings. Although optical glass usually is thought of as transparent, it can reflect up to 4 percent of any light falling on it. To lessen this percentage and improve image quality, an antireflection coating (usually of magnesium fluoride) is applied to either some or all air-to-glass

Celestron SkyMaster Pentax XCF

www.astronomy.com 71 all surfaces should be coated, so All of the binoculars here have over- “fully coated optics” is preferred. the-counter prices of $100 or less and are “Fully multicoated” optics, where readily available from local merchants or every optical surface has by mail order. All come with the same been coated with several basic accessories, including soft carrying microscopically thin layers cases, neck straps, and, in most cases, a of magnesium fluoride, is lens-cleaning cloth. your best choice. All are center-focus models. This Better binoculars use means when you turn a knurled dial, prisms made from bari- both focus simultaneously, um crown (BaK-4) glass, rather than each eyepiece being focused while lesser models use individually. borosilicate (BK-7) glass. But what if your eyes don’t come to BaK-4 prisms transmit the same focus? Not to worry. The right brighter, sharper images eyepiece on each of these binoculars can because their design be focused independently of the center passes all the light that focus mechanism. The table on page 71 enters — what’s known summarizes each binoculars’ statistics as “total internal reflec- and features. tion.” Due to their opti- cal properties, BK-7 Testing with both eyes Orion prisms suffer from light To find out if some binoculars are better WorldView fall-off and, consequently, than others, I tested them head-to-head. slightly dimmer images. I checked for optical aberrations during Besides their optical qualities, binocu- the day as well as at night. lars should be comfortable to look Field curvature and distortion are through and hold. You shouldn’t have to checked most easily during the day on hold binoculars far in front of your eyes terrestrial targets. Distortion causes surfaces of binocular lenses. While a sin- or scrunch them in close to take in the straight lines to bow or curve, while field gle coating is good, multiple thin coat- full field of view. curvature causes different parts of the ings are even better at enhancing the The distance between the eyepieces view to focus at different settings. unit’s optical performance. and your eyes is called eye relief, and it is Viewing celestial objects at night will So-called multicoated binoculars, usually expressed in millimeters. The give you a pretty however, typically have only the outer binoculars featured here good indication lens surfaces coated. For the best views, have eye relief ranging of binoculars’ from 9mm to 24mm. If image brightness, you must wear glasses astigmatism, and Phil Harrington is the author of the new observ- ing guidebook Star Watch, which is published by when observing, stick to contrast. John Wiley & Sons. the high end of the range.

Oberwerk 8x56 Oberwerk 11x56 Astigmatism, which causes stars to focus ($90) binoculars are as bright as as extended lines rather than points, is in the Nikon 10x50, although most noticeable in the periphery (edges) the Bushnell and Pentax of the field of view. models have a bit less So, how did they perform? All of the image contrast. binoculars showed some degree of each Distortion and astigma- aberration but performed surprisingly tism also are more pro- well considering their low prices. nounced than through I judged the Orion Scenix 10x50 the , blurring ($90) a cut above the rest for excellent the outer third of each image contrast and brightness. Focusing field. Both the Bushnell is smooth and precise, and images are and Pentax binoculars sharp and clear. Distortion and field cur- are easy to hold, how- vature are evident around the outer ever, and focus 25 percent of the field of view, which is smoothly. less than most in this price range. The Tasco’s Sonoma view through the Scenix 10x50 compared binoculars ($60) also favorably to my Orion UltraView 10x50 have good image binoculars, which cost $70 more. brightness and con- The Nikon 10x50 Action binoculars trast. Field curvature, Swift Aerolite ($100) also are exceptional. Aberrations however, softened the outer are well-corrected, as evidenced by a half of the field of view when the inner sharp, flat field of view and good image half was focused, and vice versa. contrast. I also like Nikon’s bayonet-style Ergonomically, I found the Sonoma’s (the appearance of eyecups that twist out rather than fold tapered eyecups to be the most comfort- faint, duplicate images) like all the others. Ergonomically, the able as well as the most effective at around brighter objects. The ghosting is binoculars have a sculpted feel that blocking stray light. The eyecups worked likely an artifact caused by irregularities makes holding them easy. well even when I purposely observed in the paint inside the barrels of the par- Images through the Bushnell 10x50 near a streetlight. The binoculars I tested ticular binoculars I tested. Several spots Legacy ($99) and Pentax 10x50 XCF had traditional multicoated optics, but around the internal field stop looked as many retailers sell a different version that though they had been touched up with includes ruby-coated lenses. Ruby coat- less-than-flat black paint. Focusing, how- ings, designed to reduce glare in ever, was smooth, and the unit was com- bright lighting, are not suitable fortable to hold thanks to conical barrels. for stargazing. Not only do the Oberwerk 8x56 Images in the Oberwerk binoculars ($100) look the same as the 11x56 binoculars ($100) also 11x56 model, but the field of view is were sharp, although I saw practically the same. While 6° is a wide some minor ghosting field of view for 11x binoculars, it’s a bit

Nikon Action Tasco Sonoma

www.astronomy.com 73 /// CONTACT INFORMATION

Bushnell Corporation Nikon Pentax Imaging Company 9200 Cody 1300 Walt Whitman Road 600 12th Street, Suite 300 Overland Park, KS 66214-1734 Melville, NY 11747 Golden, CO 80401 [t] 800.423.3537 [t] 800.645.6687 [t] 800.877.0155 [w] www.bushnell.com [w] www.nikonusa.com [w] www.pentaximaging.com

Celestron International Oberwerk Swift Instruments, Inc. 2835 Columbia Street 2440 Wildwood 952 Dorchester Avenue Torrance, CA 90503 Xenia, OH 45385 Boston, MA 02125 [t] 310.328.9560 [t] 866.244.2460 [t] 800.446.1116 [w] www.celestron.com [w] www.bigbinoculars.com [w] www.swift-optics.com

Eagle Optics Orion Telescopes & Binoculars Tasco 2120 West Greenview Drive P. O. Box 1815 9200 Cody Middleton, WI 53562 Santa Cruz, CA 95061 Overland Park, KS 66214-1734 [t] 800.289.1132 [t] 800.676.1343 [t] 800.423.3537 [w] www.eagleoptics.com [w] www.telescope.com [w] www.tasco.com

base of the prism housing swings the was able to hold the SkyMaster by hand filters in and out. Urban stargazers long enough to enjoy views of many of might benefit from this feature, but I my favorite sky objects. Although images didn’t see a big difference from sub- were a little soft across the outer 25 per- urban or rural settings. cent of the field, the overall effect was While Swift’s Aerolite binoculars striking. If you are in the market for ($81) are comfortable to hold, the giant binoculars at an economical price, thin focus wheel is a little more diffi- I recommend Celestron’s 15x70 cult to use than the focusing wheels SkyMaster binoculars. on the other binoculars. Contrast is Indeed, all of the binoculars presented good, although image brightness here offer exceptional value for the isn’t as high as through some of the money. As in the telescope market, other models. The outer third of the binoculars that contain advanced features field of view also produced soft are readily available at amazingly low Celestron images due to field curvature. The prices. The models featured here certain- OptiView LPR Aerolites also are the only binoculars I ly prove you don’t need to break the tested without a tripod socket built into bank for binoculars that will serve you the central hinge. well for years to come. X Celestron’s 10x50 UpClose binoculars narrow for 8x. The small field creates a ($37) are the least expensive in this noticeable tunnel-vision effect I found group. Despite the low price, images are confining. Even though the image con- more than satisfactory for someone just trast is good, and stars are sharp across starting out. Admittedly, contrast is 80 percent of the field, I preferred the lower and astigmatism is greater than 11x56s for the above reason. in some other models. However, pro- The Celestron OptiView LPR ($100), viding beginning observers fully coat- Orion WorldView ($40), and Eagle ed optics for under $40 is a great Optics Triumph 10x50 binoculars ($99) manufacturing accomplishment. all produce good image brightness and Finally, we come to Celestron’s contrast, although not quite to the level giant 15x70 SkyMaster ($88), which of the previous models. All had sharp I left to the end because their size images across the inner 75 percent of puts them in a different league than their fields of view as well as acceptable the rest. Image brightness, quality, contrast and sharpness. And here’s a and contrast are all remarkable con- twist: Celestron’s OptiView binoculars sidering the bargain price. Usually, you Celestron have built-in broadband light-pollution should mount binoculars of this size on a UpClose filters. Turning small thumbwheels at the tripod to get the most out of them, but I

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