Binoculars or field glasses are optical instruments for providing a magnified view of distant objects, made up of two identical telescopes mounted on a single frame. Most binoculars have two prisms in each side. By bouncing the image back and forth, the binoculars can be much shorter than a single tube telescope which produces the same size image. At the same time the view lenses can be wider than the eye pieces, allowing a wider field of vision. Modern binoculars also allow each side of the binocular to be focused separately so a sharp image can be seen by the viewer. The separate images seen by both eyes also give a 3-dimensional view with good depth perception.
What to Look for
Cheaper binoculars, like opera glasses, use only convex and concave lenses for viewing and have little magnification. Better binoculars use prisms to give more magnification.
The numbers on a set of binoculars show magnification and light gathering ability. A 7X35 set of binoculars gives a magnification as if the viewer were 7 times closer to the object viewed than he is, and the objective lens is 35 millimeters in diameter.
Lens coatings can significantly reduce the light loss and yield a clearer image for the viewer. Coated 7X35 lenses can give nearly as good an image as uncoated 7X50 binoculars.
Common Pitfalls
Light, easily portable binoculars will never give as good a magnification as movies sometimes suggest. Neither do they give an overlapping figure-8 view, but rather a 3-dimensional circle of viewing.
Going to a larger magnification however, adds the problem of vibration for hand-held binoculars. Greater magnification requires the use of a tripod and dampening mechanisms so changing the direction of viewing makes a smooth transition from object to object.
Because of the problems of light gathering, vibration and weight, especially for hikers, anything above a 10X50 magnification and lens opening is likely to be disappointing. A pair of traditional 7X35 magnification with coated lenses may be the best way to go.
Member Comments