Optical Features
Aperture :
The important specification is the diameter of the front lenses. Binocular intended for the daytime use, where plenty of light is available, the aperture is not critical. Binocular with 20mm, 21mm, 25mm, 30mm, 35mm-front aperture lens works well in the daytime. When it comes to night time astronomy use, binoculars with at least 40mm, 50mm, 60mm or 80mm lenses are the best. To determine binoculars with such number 7x50 or 10x50. The last number “50” is the aperture in millimeters. Larger the number, the brighter the images will appear. The tradeoff is that the bigger the aperture, the bigger and heavier, and more expensive would be in term of purchases.
Magnification :
In a binocular 7x50 or 10x50, the first number  “7” or “10” is the magnification. Binocular comes with magnifications from 7x to 20x. Here the high power is not the advantage you might think. As you increase the power , you decrease the wide field of view as well as the optical quality. It is also very difficult to hold the binocular steadily and so one cannot see the detail clearly as it is shaky. The most popular magnification in use for astronomical purpose are 7X to 10X.
Actual Field of View :

Field of view is often given in “feet at 1,000 yards” or “meters at 1,000 meters”. This number will tell you how wide an object will completely fill the field if it were 1,000 yards or meters away. In astronomy we are looking for the object across the sky. Field of view measured in degrees makes more sense to us. A field of 5 degrees for e.g. shows 10 full moon diameters. To convert “feet @ 1,000 yards” into degrees, divided by 52.5. To convert from “meters @ 1,000 meters,” divide by 17. A binocular said to give a field of 367 feet at 1,000 yards, a common number, will produce an angular field of 7 degrees. A binocular with a field of 120 meters at 1000 meters will also yield a 7 degree field. A field of 5 to 7 degrees is normal for most 7X binoculars. Wide angle binoculars may show 8 to 10 degrees of the sky.

  • Here the Olympus 10x50 gives 6.5 degree field of view.
  • Here the Olympus 8x40 gives 8.2 degree field of view.
  • Here the  Olympus 7x35 gives 9.3 degree field of view.
7 x 21 / 8 x 21 / 10 x 21 / 10 x 25 / 7 x 35 / 8 x 40 BINOCULAR
If you are a bird watcher or a fast sports lover, these Binoculars are for you. Fully coated optics provide crisp brilliant images in day time illuminations. Excellent for skiers, hunters, panoramas viewing or mountain climbers.
7 x 50 / 10 x 50 / 12x50 / ALL PURPOSE BINOCULARS
The most popular combination of Power & Size, excellent versatility for general use. You will get bright clear images exceptional good for bird watching, boating, hunting, sports, touring and star gazing at ease.
16 x 50 / 20 x 50 / 10-30x60 zoom / 20x80 / BINOCULARS EXTRA MAGNIFICATION
For the occasions when extra power is needed. Recommended for use under good light condition (To be used with tripod).
For steadier, more comfortable viewing.
The best way to improve the view through binoculars is to place them on a tripod. A steady image will reveal smaller details such as the moon of Jupiter and small star clusters.
Mount any powerful binocular with a thread 1/4" - 20 thread socket to a standard camera tripod.
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