Binoculars for Astronomy
Binoculars are probably the best type of optical instrument for the beginning astronomer . They are much less expensive than a telescope and a wide field of vision. They are also very easy to use and extremely portable. Binoculars are handy for experienced astronomers , too. By observing the Moon through binoculars , especially when it is not complete while the mountains and craters shadows , many lunar features can easily be witnesses. Later in the universe , many deep sky objects are visible. It is even possible to discover comets with these wonderful astronomical instruments.
Binoculars are essentially a pair of telescopes , two small short -focus, telescopes side- by-side reflective prism . They are much more comfortable to look through because you do not need to close one eye , as you do looking through a conventional telescope. Binoculars are compact because the path of the light traveling through them is folded in each monocular by the series of prisms.
All binoculars are designated by two numbers: expansion and openness. The opening is always indicated in millimeters. And seven by fifty binoculars ( 7 x 50 ) gives a magnification of seven times by two monocular taking fifty millimeter objective lenses. This is the size of the opening which is the most important parameter as this binocular limit the amount of light entering the eyes of the observer. The opening should be as broad as possible, but unfortunately, the greater the objective lenses , the heavier the instrument becomes - and therefore it is less easy to hold for long periods of time and is also more expensive.
In general , for the higher magnification binoculars pocket should be seven times , and for ease of use , with the objective lens opening fifty millimeters . Indeed , the exit pupil ( the diameter of the shaft of light emerging from each monocular ) corresponds to the diameter of the pupil of the dark-adapted eye . The exit pupil is calculated by dividing the opening of the expansion . So in this case, fifty divided by seven equals seven or so, and a dark-adapted eye is about seven millimeters in diameter , hence why I say 7 x 50 binoculars are best for astronomers .
Prisms inside the binoculars are two designs : roof prisms or Porro prisms . The former are lighter and smaller than Porro prisms and are not really good for observing the night sky . Porro prism binoculars are by far the best , especially those with BaK-4 prisms . These are made of glass and barium crown are of the highest quality available. BK -7 prisms are made of borosilicate glass , but the sharpness of the image obtained from them are not both at the periphery of the field of vision compared to BAK -4 prisms .
Really good binoculars come with colorless multi-coated lenses to reduce reflection and thus increase the transmission of low light from the night sky . Avoid binoculars that have red or ruby color lenses objectives; these lenses have coatings that attempt to compensate for the lower optics.
Binoculars are a lot of development , with two optical tubes focusing simultaneously. However, the best binoculars can focus independent , which is good for people with uneven eyes ( and that means most of us ) and are therefore the best design choice. They are also very solidly built , which means they will usually survive accidents such as a fall . There is nothing more useless than monocular binocular misaligned.
