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Tuesday, April 29, 2014

Gadget Bag: Compact Binoculars

10x25 sport optics provide high power in a camera bag-friendly size

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There are a large number of choices when it comes to binoculars. Companies are continually increasing the quality of their optics, glass coatings, weatherproofing and focus range while also expanding their model sizing. While this proliferation keeps competing manufacturers producing the most up-to-date tools, it can make purchasing decisions overwhelming.

To slim down the field, let's look specifically at 10x25 compact binoculars. Advanced birders may be particular about the size and magnification they use to match their preferences, but for multipurpose photographers interested in travel-friendly binoculars, 10x25 compacts are a go-to for several reasons.

The 10x magnification strength is great enough to provide visibility for distinguishing animal markings, but not such a high strength that a tripod becomes necessary for steady viewing. Handheld use (and general portability) is a strong suit of the 10x25s, as these compacts tend to be lighter than larger- and smaller-magnification binoculars because of their specific optics.

When looking at different brands of binoculars, there are several factors to note to find your best match. The first factor is the prism. Prisms act like mirrors to shorten the optical path, allowing binoculars to become smaller, as well as flip the image right-side-up after it has been inverted by the optics. Two types of prisms are used.

Porro prisms have a Z-shaped optical path, as the objective lens is slightly askew from the eyepiece, giving a greater depth perception and wide field of view. All the surfaces are reflective, providing no light loss. But porro prisms take up more space than roof prisms. For this reason, the majority of 10x25 compacts utilize a roof-prism design. In roof prisms, the objective lens and eyepiece are in alignment and the optical path is a bit longer. Some roof prisms employ BaK-7 glass, but BaK-4 is considered premier quality. There's some light loss with roof prisms, so various coatings are used to minimize this loss.

Roof prisms split light into two paths, then reconnect the image. This split has the potential to cause polarization. To negate this effect, many manufacturers add a phase-correction coating. Anti-reflective coatings are also used to reduce light loss and increase contrast. Adding this can make a huge difference, upgrading smaller-objective lenses with the coating to have a noticeable advantage over large-objective lenses without it. Multicoated binoculars have antireflective coatings on one or more surfaces. Fully coated models have a single antireflective coating on air-to-glass surfaces.

Within the group of 10x25 compact binoculars, each pair will have a varying field of view, close-focus distance, level of weatherproofing, and be within a different budget bracket. Here are several options to explore for meeting your binocular needs.

The Brunton Echo Compact Dual Hinge binoculars use a polymer frame with an ergonomic body armor to house a BaK-4 roof prism with full multicoating. The 7.8-ounce optics use a fold-down eyecup and provide a field of view of 424 feet at 1,000 yards, with a 12-foot close focus. www.brunton.com

Bushnell H2O
Bushnell's Legend Ultra HDs utilize ED prime glass and a BaK-4 roof prism with PC-3 phase coating, Ultra Wide Band Coating and fully multicoated optics. In addition to being waterproof and fogproof, the binoculars also have a Rain Guard HD permanent water-repellent lens coating. At 8.1 ounces, they have a field of view of 285 feet at 1,000 yards and a 6-foot close focus. The Bushnell H2Os are ready for wet weather, as they're 100% waterproof with an O-ring seal and nitrogen-purged to negate fog. The rubber armor secures grip and increases shock absorption. Featuring BaK-4 roof prisms and multicoated optics, the 10.23-ounce optics have a field of view of 342 feet at 1,000 yards and a 15-foot close focus. www.bushnell.com

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