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
The possibility of manual
adjustment of the sight from parallax, by the user himself. For this purpose, the design provides a corresponding regulator.
Parallax in this case is a phenomenon when, when the eye deviates from the optical axis of the sight (from the center of the eyepiece), the aiming mark visible to the shooter also shifts, while the sight itself remains motionless. As a result, if the eye is not exactly in the center, the visible position of the mark does not coincide with the actual aiming point. This phenomenon is especially pronounced in optical sights (see "Type"), and many collimators are also subject to it, although not to the same extent (but "night vision" and thermal imagers are free of this drawback, since the mark is displayed on the built-in display).
To eliminate this phenomenon, a specific adjustment is used - parallax adjustment. It is usually done right at the factory. However, the sight can be adjusted from parallax only for a certain distance, and with significant deviations from this distance (more than 30% downwards or 60% upwards), this effect begins to manifest itself again. It can be compensated for by an ideal insert ("eye strictly in the center"), but even for experienced shooters this can be difficult, especially when shooting standing, offhand and in other uncomfortable positions. In light of this, some models also provide manual parallax adjustment - a regulator that allows
...you to set the adjustment distance at the user's discretion. In addition to the situations described above, this function will be especially useful for novice users, as well as for high-precision shooting at long distances.
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 for fine-tuning the focus in the form of wheels are installed.Mounting ring diameter
The diameter of the mounting rings for which the closed-type sight is designed (see "Design").
This parameter directly determines the compatibility of the sight with a particular mount: the diameter indicated in the characteristics of the sight must match the actual size of the rings, otherwise normal use will be impossible. However, you only have to pay attention to the size of the rings if the mount
is not supplied with the kit, or if you plan to use a third-party mount instead of the standard one. At the same time, we note that the rings are available in standard sizes, this simplifies the search for suitable solutions; the most popular options are
25.4 mm and
30 mm, less often (mainly in low-cost models)
19 mm is found.
