In an emergency situation, a good pair of binoculars may turn out to be an extremely important item. It extends your sight and lets you observe the movement of people or game at a distance. A good pair of binoculars will help your vision in low light or even moon light.
Finding a good pair of binoculars is important. It requires some understanding of optics. Companies like Celestron, Leica, Minolta, Nikon, Pentax, Steiner, Swarovski, and Zeiss have spent decades earning a good reputation for high quality optical products. Tasco, Jason, and Bushnell are examples of companies that have built a reputation on low price. As with most things, you get what you pay for.
Today I see a lot of cheap binoculars selling for $40-50 that are made in China, they are junk and are not to be trusted in an emergency.
What you should look for in a pair of binoculars
The first thing to understand is that binoculars are just two small telescopes mechanically linked together. When you go to purchase binoculars you will see numbers such as 7X42 on them. This provides you with a lot of information.
The first number 7 referrers to the magnification. A magnification of factor 7, for example, produces an image that make it look like you are 7 times closer to the object.
The second number will be the size of the objective lens or front lens. A 7×42 binocular has an objective lens of 42mm. The diameter of the objective lens determines the light gathering properties of the binoculars. The greater light gathering ability of a larger lens translates into greater detail and a clear image. This is especially useful in low light conditions and at night.
Field of view:
The size of the area that can be seen while looking through a pair of binoculars is referred to as the field of view. It is usually marked by how many feet (meters) in width will be seen at 1,000 yards (or 1,000 m). The larger the magnification, the smaller the field of view. A larger field of view translates to a larger area seen through the binocular.
Relative brightness index (RBI)
RBI measures image brightness. It is determined mathematically by squaring the exit pupil. Binoculars marked 7×35 have a 5mm exit pupil (35/7=5). So their RBI is 25 (5×5=25). A RBI of 25 or greater is considered best for use in dim light.
Doubling the size of the objective (front) lenses quadruples the light gathering ability of the binocular. A 7×50 binocular has four times the light gathering ability of a 7×25 binocular.
Most good binoculars have antireflection coatings on their glass surfaces. These coatings assist light transmission. The better the coating, the better the light transmission. You can learn a lot by the way the manufacturer describes his coatings. “Coated,” means a single layer of antireflection coating on some lens elements, usually the front and last lens. “Fully Coated” means that all air to glass surfaces are coated. “Multi-Coated” means that some surfaces (again, usually the first and the last) have multiple layers of antireflection coatings. “Fully Multi-Coated” means that all air to glass surfaces have received multiple layers of antireflection coatings, and this is the best. It is also the most expensive.
For dawn to dusk field operations, a 4mm to 5mm exit pupil is usually satisfactory and 6×30, 7×35, 8×30, or 9×35 binoculars are probably the most useful. They are bright enough to allow you to see in shadowed areas and dim light, and compact enough to not be a burden to carry. Higher power binoculars are hard to hold steady without external support. Binoculars with an objective lenses of 40mm or larger tend to be heavy and bulky.
If you are hunting in the woods you will want binoculars with a large field of view, like a 6×30. In the mountains or plains a hunter will probably favor higher power, since he will be able to spot game at greater distances. Binoculars in the range of 8×30 or 9×35 would serve well. A pair of the most common 7×35 size binoculars is probably about as good for all-around field use as any.
Good binoculars can cost up to a thousand or so dollars. Unfortunately, most of us don’t have this kind of money. So I will offer a few suggestions. Decent Nikon binoculars can be found for around a hundred to two hundred dollars. Even at this low price, Nikon seems to maintain their quality.
Another suggestion is garage sales. Every now and then I come across a pair of old Sear or J C Penny binoculars for $5 or so. I disassemble them and give them a good cleaning and they are surprisingly good. They make a good spare pair. They are much better than a lot of the Chinese junk.
Hope this helps you. I will cover night vision in the future.