Here is a article on my blog. Please share your opinions.
There are basically two kinds of binoculars:

Binoculars with Porro Prisms (M-shaped) and Binoculars with Prism Roof (H-shaped). In the past all binoculars had Porro prisms. In recent years, however, the new roof prism versions have appeared, whose idea was to first create smaller binoculars and easier to handle. With regard to the optical quality of the two types, there is no difference today (but some still believe that Porro binoculars have a better stereoscopic perception due to the distance between the lenses). Porro binoculars are still larger than the others. The price of Porro binoculars is always lower than the others, so if you are willing to carry a bigger and harder binoculars with you, you can often buy very good Porro binoculars at acceptable prices for Roof.

1. The most important aspect is the quality of lenses and eyewear

a) Coating (or antireflex). The coating layer is to minimize the light loss that occurs when the light comes in contact with an untreated glass. Even when the glass is perfectly treated, there is often a loss of brightness of ca. 5%, loss which can be minimized by treating anti-reflex lenses. Zeiss is the first company to discover the anti-reflex system in the 20-30s. Coating appears under different names:

[b] -CO (coated optics) [/ b] means that the binocular has one or more lenses that are treated with anti-reflex.

-FC (fully coated) means that the binoculars have all lenses treated with anti-reflex.

-MC (multi coated) means that the binocular has one or more lenses treated with multiple anti-reflex layers.

-FMC (fully multi coated) means that the binocular has all lenses treated with multiple anti-reflex layers. The more the better the quality.

-PC-3 (phase coating) treatment that further enhances the optical quality of lenses resulting in better and clearer resolution. It is not used for Porro binoculars but only for Roof.

b) HD (high definition) lenses with extremely good quality, where the contrasts are almost perfect, higher brightness and clarity is uniform over the entire surface of the lens. (used inter alia by Swarovski and Leica)

c) FL (fluorite) fluorite lenses. They have virtually the same role as HD (used by Zeiss and the new Leica model)

d) ED (extra low dispersion) Not as advanced as those with HD but better than FMC lenses (often used by Pentax and Nikon).

2. Inside Writings

BAK-7 and BAK-4 (Barrium Crown) upper prisms that increase the ability to absorb more light. BAK-7 are good, BAK-4 are even better. All quality binoculars are used today by BAK-4.

3.Lensime / Brightness Diameter

The larger the diameter, the brighter and brighter the image will be. It is always preferable that the brightness is as big as possible. The problem is, however, that with the increase in lens diameter, the size of the binoculars also increases. The most commonly used sizes are 20.25mm (pocket binoculars), 30.32mm, 40.42mm, 50mm and 56mm. Some brands like, for example, Bushnell and Pentax also use 43mm and 45mm Zeiss (for example, their new RF binoculars).

4. Chromatic Aberration

The worst quality lenses can be seen when the light passes through a lens (violet, red, green) through the lens through the lens. It’s a very annoying, unpleasant and unwanted problem. Pt. to avoid such problems, in addition to the above methods, acromatic or apochromatic lenses are used which, combining positive and negative lenses, add the light rays into a concentrated bouquet, thus creating a picture as perfect as possible without the influence of certain colors the rainbow

5. Collimation

The parallel alignment of the inner prisms creates a balanced image for both eyes. A wrong collimation (a misalignment of prisms) will directly create a double image in binoculars. Always a nightmare!

6. Field of view

It measures either in degrees, or in yards, and is an area that can be observed at a certain distance. For example. a 6-degree visual field means that 1000m shows an area of ​​approx. 105m and so on. The visual field is diminishing as magnification increases. So if you are interested in a wide field of vision, a Porro binoculars (known as larger visual fields) are indicated 7×50 or 7×56. Generally, all 8×2 and 10×2 binoculars have visual fields of 6-6.5 degrees, between 105 and 120m at 1000m. Poor quality binoculars have miserable visual fields creating a tunnel sensation.

7. Eye Relief (focal length)

It is the distance between the eye and eye where the eye gets a full field of vision. Often very useful for those who wear glasses and all other users.

8. Exit pupil (exit pupil)

The size of the circle of light passing through the eyepiece. The higher the exit pupil, the clearer the image. The exit pupil is very important and many do not take it into account. What’s the point of taking a binoculars that have good diameter lenses, acceptable quality, but a low exit pupil? The picture will not be what it could have been. Do not forget about it when you buy binoculars !!!

9. Lot Tec, Rainguard, etc.

Ways of treating lenses that on the one hand make the lens more resistant to dirt and dust and on the other hand it prevents the lens from getting wet. If it rains, the drops of water will be divided into very small particles that will slide lightly on the lens, leaving no traces of it and at the same time allowing a good clarity of the image in spite of rain or fog.

10. Waterproof / Waterproof

Some binoculars are resistant to water droplets but do not cope with long-lasting humidity (eg if you have a binocular in your car all the time) or long water contact. These are defined as Waterresistant.

Waterproof are often nitrogen-filled binoculars (a gas drier than air) and sealed with an O ring. These two ensure that binoculars face wetness, rain and even the situation where it is dropped in the water but does not get too deep without the binoculars steaming inside. Always prefer such binoculars. Several companies have begun to experiment with Argon and Krypton to make binoculars more resistant to temperature changes.

11.Focus

Center focus – clarity is adjusted by means of a focus wheel often placed between binoculars. It must be adjusted at all times when the distance to which the binoculars are concerned increases or decreases.

Autofocus is adjusted with diopters. Once adjusted, it remains the same regardless of the distance it is looking at. Autofocus binoculars are often less optic than those with centerfocus.

12. Diopter

It is often adjusted by turning the right eyepiece of the binocular, followed by the focus adjustment. The newer binoculars adjust in the middle, just like the centerfocus. With autofocus binoculars, diopter adjustment is available on both the right and left eyepieces, as well as on some more advanced binoculars. The central diopters are the best ones to be blocked. This way it is not disturbed when the binoculars are used. Dioptres generally range from -3 to +3, but there are binoculars where diopters are adjusted from -5 to +5.

13. Magnification

How close is your image. It is always defined by a digit followed by an X. So 8×42, 10×56, 7×50 means a 8x, 10x or 7x magnification and 42: 56 and 50 lens binoculars.

14. Variable measurement

Some types of binoculars, like the ribbons, appear with variable magnifications (eg 8-15×50). NOT RECOMMENDED! All binoculars with variable magnifications have poorer optics than fixed ones, are more difficult to handle, and often create a feeling of vomiting or headache resulting from the fact that the eye is harder to force, trying to focus the image.

15. “day” and “night” binoculars

There are some types of binoculars that are built for. to use more at certain times of the day. Generally speaking, binoculars whose lenses have a greenish shade (say lenses and not the image) are most effective in daylight hours, while binoculars that have a more reddish hue of lenses better fit their use over time night (eg Steiner Nighthunter).

16. Marine, military, binoculars, range finder and BIS

Marine binoculars are not recommended with magnets larger than 7x due to the fact that older people shake the picture too much to make it harder to use. On heavy tonnage ships it goes magnificently up to 10x, but it is still 7x. 7×50 is the classic type of marine binoculars. Marine binoculars often have compasses.

Military binoculars often have a gradation scale, sometimes illuminated and sometimes infrared. Optics are often weaker than some civil but generally very good quality.

Binoculars with range finder (telemetry). Civil there are basically two alternatives: Leica Geovid and Zeiss Victory T * FL RF. There are binoculars that calculate the distance to the object by laser. Zeiss Victory also has a BIS (Ballistic Information System) system that calculates the bullet trajectory. I’m useful in hunting. Leica does not have such a good optics, but Zeiss is super!

17.Monoculare

One tube instead of two. Many monoculars are equipped with a range finder.

18.Twilight factor

Represents the binoculars’ ability to cope with low light conditions. The bigger the twilight factor the better.

The perfect binoculars

A magnification of 7.8 or 10 (at magnifications over 10x begins to appear a tremor of the image that can be considered disturbing) with a brightness of at least 42mm to 50mm, 56mm. Perfect collimate without chromatic aberration with a large focal length with a large exit pupil with a large twilight factor with central focus and blockable diopter head with adjustable eye caps very well rubberized, but with a FMC HD or FL lens, with a neoprene strap whose hoods stay in the outside of the binoculars, easily adjustable, eyeglasses that remain hanging on the belt and protection for lenses to stay on binoculars all the time.

Avoid binoculars with great magnificence but small diameter lenses. The image will be blurred, darker, weaker contrasts. The following magnification-brightness combinations are recommended:

7×40, 7×50, 8×30, 8×40, 8×42, 8×43, 8×45,8×50, 8×56, 10×40 (only for high performance binoculars, eg Zeiss, Steiner etc), 10×42, 10×43, 10×45, 10×50, 10×56. On binoculars over 10x you avoid a diameter smaller than 42mm and those of 15x not less than 56mm.

Binoculars of type 8×20, 8×25, 10×25, etc. are good only if they are produced by the strongest companies that compensate for the small diameter of the lens with a very good quality, the image being weaker but compared to other excellent ones.

Binoculars such as 20×50, 16×42, 10×20, 10×25, 10×30 and others like this are not recommended. Some exceptions being to binoculars in the upper classes.

Avoid binoculars with BAK-7, or non-FMC lenses. So are those that are not waterproof and sealed with an O ring.

Not long ago I had an exchange of views with Holger Merlitz, an astrophysics professor considered to be one of the great gray matter in terms of binocular knowledge. He shared something I did not know, namely that the materials Zeiss, Leica and Swarovski make their lenses are related to precious stones. In other words, materials that are already very early in the process are very pure and very resistant. It confirms a suspicion I have had for a long time, namely that there must be another secret behind their success in making their “bottles”. Nikon, Steiner, Kowa, among others, theoretically use the same lens treatment methods and yet they do not manage to create the same things. It seems, therefore, that part of the secret is constituted by the quality of the materials with which it works.

That is why, and not only, I still have to say that there are only three companies that can place themselves in the binoculars:

Zeiss, Swarovski and Leica. Between them and the others there is a fairly large distance, although binoculars such as Leupold, Nikon EDG, Kowa Prominar, Steiner Peregrine or Nighthunter seem to approach them.