Field of view at 100 m
The diameter of the area visible through the sight from a distance of 100 m — in other words, the largest distance between two points at which they can be seen simultaneously from this distance. It is also called "linear field of view". This indicator is more convenient for many users than the angular field of view (the angle between the lines connecting the lens and the extreme points of the visible image) — it very clearly describes the capabilities of the device.
In sights with magnification adjustment (see above), both the entire range of width — from maximum to minimum — or only one value of this parameter can be indicated. In the latter case, the largest width of the field of view is usually taken, at the minimum magnification.
Parallax adjustment
Optical sights with
parallax adjustment can be equipped with a wide ring on the AO (Adjustable Objective) lens or a drum on the SF (Side Focusing) control unit, on which additional accessories are installed for fine-tuning focusing in the form of wheels.
Weapon compatibility
The weapon class that this scope can be used with.
Different classes of weapons differ in the energy of the shot and, accordingly, the recoil force that the sight must endure without consequences. It is the maximum allowable energy of the shot (muzzle energy) that in this case is the main criterion for classifying the sight into one of the categories:
light pneumatics,
rifles and shotguns,
large caliber. It is worth saying that such a division is somewhat arbitrary — see details in separate paragraphs; here is their detailed description:
— Lightweight pneumatics. Sights designed for weapons that practically do not give recoil — such as air PCP rifles, spring-piston “breaks” with muzzle energy up to 7.5 J, carbines chambered for Flaubert, as well as airsoft drives. Such models are definitely not suitable for firearms: they do not tolerate even the recoil from small-caliber rifles, not to mention more serious use. And even pneumatics have their limitations — in particular, powerful (more than 7.5 J) spring-piston models give significant returns with strong vibrations, and in pistols with the Blow-back system, noticeable concussions occur not because of the shot itself, but from -for the work of automation. So it is better to equip these types of weapons with more durable and reliable sights.
— Rifles and shotguns. Sights that can be used with
...rifles of small and medium calibers, as well as smoothbore weapons (shotguns). They have a solid construction that allows them to endure rather strong recoil and accompanying vibrations without consequences, but the specific restriction on the allowable muzzle energy (and, accordingly, the calibers and ammunition used) may be different. However, scopes in this category are usually able to safely carry at least 2500 J — this is enough for rifled calibers 5.45x39, 7.62x39 and .223, as well as for 12-gauge rifle cartridges with a standard weight of gunpowder. And in many models, the maximum allowable energy can reach 3500 J and even 4000 J (the smallest values \u200b\u200bnecessary for full-fledged use with .308 and 7.62x54R calibers, respectively). At the same time, for reinforced magnum ammunition, as well as for some powerful (though not large) calibers, such a sight may still not be enough.
— Large-caliber. The most durable and reliable sights, designed for muzzle energy of 4000 J and above. Because of this, they can be used even with large-caliber firearms, as well as with some powerful calibers that are not formally large — for example, .300 Win and .338 Lapua Magnum. The specific restriction on muzzle energy, again, may be different, but if you are looking for a sight for a caliber more powerful than 7.62x54R or for reinforced rifle ammunition like 12x76, you should definitely pay attention to this category.
Separately, it is worth noting that “firearm” sights, even quite durable and reliable, are not recommended to be installed on pneumatics with a spring-piston mechanism or a gas spring. The fact is that such rifles have a specific recoil, directed forward rather than backward, moreover, giving sharp vibrations in different directions; and although the force of such recoil is low, it can still adversely affect the sight, which was not originally designed for it.Sight length
The total length of the sight.
This parameter is important primarily for optical sights (see "Type"). Such devices can be quite large — from
20 – 30 cm in the most compact models up to
40 cm or more ; and the distance from the eyepiece to the eye when aiming must be strictly defined. So before buying, it's ok to clarify whether it will be possible to correctly place the selected model on the weapon. But collimators, even the largest ones, are very compact, usually there are no problems with their installation, so in such models the length does not play a special role.
