![]() BK-7 prisms (borosilicate glass) are also good quality, but brightness falls off slightly at the edge of the field compared to BAK4. What’s the difference between BAK4 and BK-7 prisms?īAK4 prisms (barium crown glass) are the highest quality available. The recommended magnification range for the BT-100XL-ED is from 25x to 80x. Therefore binocular telescopes don’t mention magnification in their model designation, but do include the objective diameter (100mm in this case). Binocular telescopes have interchangeable eyepieces, and it’s the eyepiece focal length that determines magnification. So what’s the magnification of a BT-100XL-ED? Binoculars using multiple fixed-power eyepieces do not suffer from the optical limitations of zoom binoculars. Our 25/40×100 Long-Range Observation binocular for example, has 25x and 40x eyepieces on rotating turrets, so you can easily switch back and forth between 25x and 40x magnification. On the other hand, if the numbers are separated by a “/”, then the binocular is not a zoom, but uses multiple fixed-power eyepieces to obtain different levels of magnification. See “ Just Say No to Zoom Binoculars” for more information. Note: We do not recommend zoom binoculars. If the numbers are separated by a “-“, such as “12-36×70”, then the binocular is a “zoom”, and the magnification is continuously variable from the first number to the second number (in this case, 12x to 36x), by moving a zoom lever. When there is more than one number before the “x”, this means the binocular has multiple levels of magnification. But as objective size increases, the physical size and weight of the binocular increases, and price also goes up almost exponentially. For daylight usage, the larger the objectives, the brighter and clearer the view will be. Generally speaking, for astronomy binoculars, the larger the objectives, the more you’ll see. The size of the objective lenses determines the light-gathering power of the binoculars. There are roughly 25mm in an inch, so a 10×50 binocular’s objectives are approximately 2″ in diameter. The objectives are the large lenses at the end of the binocular (opposite from the eyepieces). The second number refers to the objective size (diameter in millimeters). Objects appear 10 times larger than they do without the binocular. A “ 10×50” for example, magnifies the view by 10 times. The first number refers to magnification. The correct usage of a “pair of binoculars” would be a 10×42 Sport ED for yourself, and an 8×42 Sport ED for your spouse. We don’t view the night sky or go bird-watching with a “binoculars” or “pair of binoculars”, we use a binocular. We don’t ride a “bicycles” or “pair of bicycles”, we ride a bicycle. It’s no different than the word “bicycle”, which means “two wheels”. But the “bi” in the word binocular means “two”- in this case “two oculars” (ocular is another word for eyepiece). We’d add the word “pants”, or pair of pants to that list. We strongly disagree! All the other words in that list are objects that are comprised of two parts that work together, such as the two halves of a pliers or scissors. ![]() The Oxford Dictionary actually says the word “binocular” doesn’t exist in singular form! It only exists in a plural form, along with bellows, forceps, gallows, glasses, pliers, scissors, shears, and tongs. There is apparently a lot of dissenting opinion about this. Is it a “pair of binoculars” or a “binocular”? Kevin Busarow, President, Oberwerk Corp. But please feel free to call us at 93 or email ( ) with your questions. Welcome to Oberwerk! We’ve tried to answer some of the most common questions we receive regarding our binoculars on this page.
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