Binoculars have the advantages of clear and bright images, large field of view, easy to carry, and cheap price, and are suitable for astronomical enthusiasts to survey the sky and observe planar bodies such as nebulae, star clusters, and comets.  

If you’ve been using high-resolution, long focal-length telescopes in the past and don’t realize you’re missing out on much of the fun, try binoculars and you’ll be amazed by the beauty of your field of view.  Because binoculars have a wide range of uses, there are a wide variety of binoculars on the market and their performance varies greatly.  So in this guide, you will learn more about 8 common parameters for binoculars.  

8 common parameters for binoculars  

1. The ratio  

Magnification, the most important parameter for hand-held binoculars, is usually under 20 times. (Anything above 20 is not hand-held and requires a tripod to support it.) If someone offers you binoculars of hundreds or thousands of times, you can just walk away.  Magnification is usually labeled on the body of the telescope. For example, 10×56 means 10 times 56mm, 8×42 means 8 times 42mm, and 6×30 means 6 times 30mm.  

If you look at an object 70 meters away with a 10x telescope, you will feel that the object is only 7 meters away from you.  Anything higher than 10 will reduce the field of vision, and even a slight shake in the hand will affect the viewing experience, as well as the amount of light the telescope can bring in.  

2. Objective lens diameter  

In the case of the same lens structure and coating process, the larger the aperture of the objective lens, the more light into the telescope, the brighter the image.  Bird-watching usually uses binoculars with an objective lens of 25-50mm in diameter.  

3. Exit pupil distance  

Exit pupil distance is the distance between the eye and the last piece of the eyepiece when the entire field of view can be seen.  Its size is very important for myopia patients who wear glasses. Although they can still see a clear image after taking off the glasses and refocusing, it is very inconvenient when they need to observe the stars alternately with the naked eye and binoculars repeatedly.  

In addition, if people wearing astigmatism glasses take off the glasses, no matter how to focus are unable to see a clear image.  To see the entire field of view with glasses, the exit pupil distance should be at least 14 to 15 mm.  When the exit pupil distance is less than 8 mm, even people without glasses can feel inconvenient to use.  

4. Coating process  

The coating process can increase the transmittance, reduce the reflectivity and improve the imaging brightness of the telescope.  Usually, multi-layer coating transmittance is better than a single-layer coating, high-end multi-layer coating lenses are more transparent, reflective little, showing light green or dark purple;  And low-end single-layer coating telescope objective mirror reflective strong, coating color is red, blue, and white.  In addition, current telescopes use phase correction coatings and BAK4 prisms to further improve the image.  

5. View  

Field of vision is the diameter of a distant object through a telescope, or you can see the diameter of an object every 1000 meters away, for example, 120 meters per 1000 meters is the size of your field of vision.  

The size of the field of view depends on the optical design and magnification. Generally speaking, the field of view is larger at lower magnification, but this is not absolute. Many high-end mirrors are a special case, but in any case, the larger the field of view is better.  A small view will give a person the feeling of being inside a leopard, while a large view will give a person the feeling of being in a French window.  For binoculars of the same power, the larger the field of view, the greater the scope of the telescope.  It is recommended to select a telescope with an actual field of view greater than 5.6°.  

6. Closest focus distance  

The shortest distance at which a telescope can focus so that an image is clear is the telescope’s “closest focusing distance”. It is recommended to choose a telescope with the closest focusing distance of 3m or less.  

7. Weight  

When looking at birds in the house, we often have to walk with binoculars for half a day or even a whole day and hold binoculars up for a long time to observe birds. Portability must be considered.  For most novice birders, binoculars weighing less than 500 grams will make birding more enjoyable. It is also recommended to choose an X-shaped telescope harness with reduced pressure (pictured below) to share the weight.  

8. Waterproof performance  

The waterproof telescope can be used even in light rain without worrying about water damage.  Waterproof binoculars usually have WP, waterproof signs, etc.  A waterproof telescope usually has a hydrophobic lens with a sealed tube filled with nitrogen.  The parameter to measure the water tightness is called “water tightness”, and it is generally recommended to choose a telescope with a depth of 3m or more.  Of course, there are other standards, such as IP level, the greater the X value, the better the waterproof and dustproof performance.