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Choosing Boating Binoculars; what you need to know
Here we take a look at what you need to know when looking for Boating Binoculars. There are always new models but the inherent designs are still the same.
First thing to consider when looking at Binoculars is how we are going to use them. We mostly use them for Navigating which means we need to be able to spot channel markers. Most places specializing in Binoculars cover birding and hunting and astronomy which are too powerful for the marine environment. Boats are not stable and so anything with a power over 7 is going to have a blurred image due to hand shake or boat movement. Buy from a purveyor of Marine Boating Binoculars and make sure you try them.
How do Binoculars Work?
Binoculars work like two telescopes mounted side by side. At the front of each telescope is a objective or a field lens. This gathers light from the object you are looking at. Letís say you're looking at a lighthouse. The objective or field lens magnifies the image of the lighthouse, but it is the wrong way up. If you are using prism binoculars (they are the most popular type), a prism in each tube reverses and inverts the image of the lighthouse. In field glasses, there is a second lens instead of a prism. The light travels down the tube, and through a lens in the eyepieces, magnifying the image even further.
Binoculars are built around a frame that houses the two telescopes and are generally hinged to allow for adjustment for each person. Some binoculars are perma focus and never need adjustment. While others have a focusing wheel in the center to allow for manual focusing and a greater degree of fine tuning for sharper images. Other Binoculars have separate focusing of each eyepiece (known as Diopter Control) which allows for additional focusing.
What do those numbers mean?
Binoculars are often specified by a set of numbers such as 7 X 50 which are the most popular for boating. The first number indicates power or magnification i.e. how many times closer the object appears to you, in this case 7 times closer. The second number is the diameter of the objective lens (the larger lenses at the opposite end to the eyepiece) measured in millimeters. This determines how much light it can obtain for effective viewing. The larger the lens (higher number) allows a greater amount of light to pass through giving a brighter image. Larger objective lenses will give you the greater amounts of light but result in heavier and larger Binoculars.
Instead of the fixed variety you can try Zoom Binoculars which can be adjusted to give you varying ranges of magnification. For example, a binocular that is listed as 7-21x40mm means the zoom portion is capable of viewing at 7x power minimum and can be adjusted up to 21x power and the 40mm would be the objective lens size. Remember that magnifications over 10x - 12 xs are very difficult to hand-hold. In which case, a sturdy tripod is highly recommended.
Prisms are used to condense the viewed image for maximum magnification in a short space. Prisms recreate an image of the original that is much purer than any image you would get from multiple lenses.
There are two kinds of prisms used in binoculars: roof prisms and Porro prisms. You can tell which type of prism is used from the shape of the binoculars.
Porro prisms Binoculars are distinguishable by the narrower eye piece than the objective lens. The resulting jog in the light path being deflected through 180 degrees twice by the two prisms in the housing
Roof prisms are indicated by the two straight tubes making them more compact and easier to hold. The Porro prism rendered better contrast and was still favored by purists for a long time after the advent of the roof prism but new technology of roof prisms has improved greatly, which makes newer models a better value.
The BAK-4 prism is made of a high quality glass and produces sharp images and good edge to edge sharpness. Generally, higher quality binoculars will use BAK-4 prisms in the construction process. Phase coated prisms take it one step further, the coating process enhances the resolution and contrast of images coming through the binocular and are generally applied only on more expensive binoculars.
Points to consider when buying Binoculars
Fit; Try them on and make sue they fit your grip and fit your face comfortably. Try them out in daylight and at night if relevant.
Coatings, if you look at the water surface, you will notice the glare of the sun shining on it. Lens coatings remove glare and allow more light to enter the optics. The more coatings a pair of Binoculars have the more expensive they are. Cheaper Binoculars do not have the coatings as better models and this can account for the wild variation in prices.
Focusing; which type of focusing is best for you? Center Focus with a wheel. The center wheel focuses at the same time for your eye, or can they compensate for unequal vision. This is by means of a dioptric correction through the adjustment of one eyepiece, usually the right-hand eyepiece.
Size and weight; do you want a pair that can fit in a pocket then the Roof Prism is more likely to work.
Do you need a compass? Binoculars are more expensive with a compass but there are benefits. Try compass position relative to your grip.
Are they waterproof, do they have Flotation straps, which are very handy if they are dropped overboard?
Waterproof Boating binoculars are typically 7 x 50 rubber armored design. The 7 magnification power number makes sense, when dealing with a moving boat. The relatively large objective (50mm) lens is desired to gathering more light which translates to increased contrast.
For more on this article recommendations and diagrams see http://www.myboatsgear.com/newsletter/200798.asp
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