Prisms, Mirrors & Glass According to the folks at West Marine, binocular prisms used to invert and magnify an upside-down image, are either Porro (binoculars with a dog-leg shape) or roof prisms (with straight tube configuration that are easier to hold). It’s generally believed that Porro prisms yield superior optical performance, since they transmit more light, resulting in brighter images and provide better depth perception, because their objective lenses are farther apart. Prisms come in two glass types, BK-7 and BaK-4. BK-7 binoculars use boro-silicate glass, while BaK-4 prisms use a denser, finer barium crown glass (a.k.a. Barium Krownate), which eliminates internal light scattering and produces sharper images than BK-7. The higher quality is reflected in the price of the binoculars. Roof prisms are lighter and more compact, but they are more complex and difficult to manufacture and have more precise tolerances, so they are usually more expensive than Porro prisms. It’s been my experience that the less expensive imported $95-to-$150 binoculars typically use BK-7 glass with a lower refractive index than BaK-4 prisms, which means they bend light less efficiently. This results in a slightly dim- mer image with more distortion, especially around the edges. The higher cost marine binos in the $225 and up cate- gory typically gravitate towards using the higher quality BaK-4 glass in their prism construction and produce brighter, cleaner images. In-Focus Binoculars can feature varying methods to focus the image in view. Some offer independent eyepiece focus to com- pensate for the differences between eyes and for different distances. Center-focus binoculars typically offer one eye- piece that adjusts to accommodate the difference between your eyes. A central focus knob then adjusts both sides simultaneously for distance. Yet others incorporate both twin focus wheels, in addition to a center focus knob. There’s no right or wrong way to make this happen, only differences in the manufacturing process that you need to consider before taking the plunge.
Image-Stabilized Binoculars Some brands like SigSauer, Steiner, Si-Tex/Koden, Canon, Fujinon, Zeiss, etc. manufacture image-stabilized binoculars. According to the folks at Si-Tex, their Koden Sirius 12 is a compact, lightweight and ruggedly built binocular manufactured in Japan using premium quality lenses and internal electronic components. Their powerful 12X magnification and wide field of view are ideal for a variety of
fishing and navigating tasks. Advanced Japanese lenses minimize light transmission loss, ensuring a bright and clear field of view over a range of light and weather conditions at sea. At the heart of these binoculars is a precision built-in, 6-axis electronic gyro sensor that delivers rock-steady vision, even in rough ocean conditions. The Sirius 12 is built with an IPX7 waterproof rating, an easy-to-grip textured surface for sure handling with wet hands, plus eyepieces and objective lenses with a water and oil-repellant coating to prevent lens contamination. These binoculars also feature easy-to-adjust eyepieces to accommodate different users, as well as a large focus adjustment wheel and On/Off switch that are easy to operate, even when wearing gloves. The Sirius 12 provides 12-hours of operation on a single AA alkaline battery, with an Automatic Power Off feature after 30-minutes to further extend battery life. The low $699 price tag offers gyro stability that’s competitive with some premium standard handheld units. No matter what type of binoculars you prefer, be sure to try them out first before making the purchase.
Made with FlippingBook - PDF hosting