Comparison Barska Tactical 6.5-20x40 FFP IR Mil-Dot vs Hawke Vantage SF 4-16x44

The magnification provided by the scope. This parameter indicates how many times the image of any object in the field of view will be larger than that visible to the naked eye. For models with the ability to change the ratio (see below), the entire available range of adjustment is indicated.

Modern sights can be produced in a wide variety of magnifications, the only exceptions are collimators (see "Type") — they usually give a magnification of 1x, that is, in fact, do not change the visible image in any way; higher values are extremely rare and usually do not exceed 5x. In other types of sights, the maximum magnification from 2x to 5x means that this model is designed for very short distances of application. In turn, the most "far-sighted" devices can provide an increase of 17 – 20x and even more.

Note that a high magnification not only allows you to better view distant and small objects, but also narrows the field of view. With this in mind, the main criteria for choosing a sight by magnification are the expected distances of use, as well as the size and type of targets. Detailed recommendations on this matter for different situations can be found in special sources. And here we note that the degree of magnification significantly affects the cost of the sight — both in itself and due to the fact that larger (and, acco...rdingly, more expensive) lenses are desirable for "long-range" optics. At the same time, a low magnification is not necessarily a sign of a cheap device — in itself, it only means that the sight is designed for short distances and a wide field of view.

As for models with variable magnification, the wider the adjustment range — the more advanced and versatile the device is, the lower the likelihood that there is no suitable setting for a particular situation. On the other hand, expanding the range complicates the design, making it more expensive and less reliable.

The diameter of the objective is the front lens of the sight. This parameter is also called "aperture".

This parameter is important primarily for optical sights and their specialized varieties — "night lights" and thermal imagers (see "Type"). The larger the lens, the more light enters it, the higher the image quality and the more efficient the device will work in low light, but the more expensive such optics will cost. It is worth noting here that the requirements for the aperture also depend on the degree of magnification: in other words, especially large lenses are not required for low magnifications. Therefore, relatively small entrance lenses, with a diameter of 25 – 35 mm and even less, are found in all price categories of classical optics — from low-cost to top. And you can compare by aperture only models with the same maximum magnification, and even then it’s very approximate — it’s worth remembering that image quality also depends heavily on the overall quality of the sight components.

In turn, for night sights, especially those based on image intensifier tubes (see "The principle of operation of night vision devices"), a large aperture is fundamentally important. So a diameter of 36 to 45 mm is considered very small for such devices and is found only in some digital models, while most nightlights are equipped with lenses of 46 mm or more.

As for collimators, the size of the space that enters the scope depends mainly on the aperture. Moreover, the actual visible size can be changed by setting the sight closer or farther to the eye — the principle of operation of collimators makes this possible. Note also that for models with lenses of a rectangular or similar shape, the size of the lens is usually indicated diagonally.

The diameter of the exit pupil created by the optical system of the sight.

The exit pupil is called the projection of the front lens of the lens, built by the optics in the region of the eyepiece; this image can be observed in the form of a characteristic light circle, if you look into the eyepiece not close, but from a distance of 30 – 40 cm. The diameter of this circle can be calculated by dividing the lens diameter by the multiplicity (see above). For example, an 8x40 model would have a pupil diameter of 40/8=5mm. This indicator determines the overall aperture of the device and, accordingly, the image quality in low light: the larger the pupil diameter, the brighter the “picture” will be (of course, with the same lens quality, because it also affects the brightness).

In addition, it is believed that the diameter of the exit pupil should be no less than that of the pupil of the human eye — and the size of the latter can vary. So, in daylight, the pupil in the eye has a size of 2-3 mm, and in the dark — 7-8 mm in adolescents and adults, and about 5 mm in the elderly. This point should be taken into account when choosing a model for specific conditions: after all, high-aperture optics are expensive, and it hardly makes sense to overpay for a large pupil if you need a scope exclusively for daytime use.

The offset is the distance between the eyepiece lens and the exit pupil of an optical instrument (see "Exit Pupil Diameter"). Optimum image quality is achieved when the exit pupil is projected directly into the observer's eye; so from a practical point of view, offset is the distance from the eye to the eyepiece lens that provides the best visibility and does not darken the edges (vignetting). A large offset is especially important if the sight is planned to be used simultaneously with glasses — after all, in such cases it is not possible to bring the eyepiece close to the eye, and it must be at some distance from the glasses so as not to hit the glass due to recoil.

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.

A complex indicator that describes the quality of any optical system (including sights) at dusk — when the lighting is weaker than during the day, but not yet as dim as in the deep evening or at night. It is primarily about the ability to see small details through the device.

The need to use this parameter is due to the fact that twilight is a special condition. In daylight, the visibility of small details is determined primarily by the magnification of the optics, and in night light, by the diameter of the lens (see above); at dusk, both of these indicators affect the quality. This feature takes into account the twilight factor. Its specific value is calculated as the square root of the product of the multiplicity and the diameter of the lens. For example, for an 8x40 scope, the twilight factor would be the root of 8x40=320, which is approximately 17.8. Models with adjustable magnification (see above) usually indicate the minimum twilight factor corresponding to the minimum magnification.

The lowest value of this parameter for normal visibility at dusk is considered to be 17. At the same time, it is worth noting that the twilight factor does not take into account the actual light transmission of the system — and it strongly depends on the quality of the lenses, the use of antireflection coatings (see below), etc. Therefore, the actual image quality at dusk for two models with the same twilight factor may differ markedly.

One of the parameters describing the quality of visibility through an optical device in low light conditions. Relative brightness is denoted as the diameter of the exit pupil (see above), squared; the higher this number, the more light the sight lets through. At the same time, this indicator does not take into account the quality of the lenses and their coatings used in the design. Therefore, comparing two sights in terms of relative brightness is only possible approximately, because even if the values are equal, the actual image quality may differ markedly. Also note that it makes sense to pay attention to this parameter only if the sight is planned to be used at dusk.

As for specific values, in the "dimest" models, the relative brightness does not exceed 100, in the most "bright" it can be 300 or more. Detailed recommendations regarding the choice of this parameter for certain conditions can be found in special sources. Here it is worth mentioning that the relative brightness is not directly related to the price category of the sight: models similar in this indicator can vary significantly in price.

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.

The presence of a diopter correction function in the sight. This feature will be very useful if you wear glasses due to nearsightedness or farsightedness. By setting the required number of "plus" or "minus" diopters on the adjustment scale, you can look into the eyepiece with the naked eye and see a clear picture — the optics of the device will provide the necessary correction. This is much more convenient than watching through glasses (especially considering that due to the recoil of the weapon, it is impossible to keep the scope close to anything, whether it be the eye socket of the shooter or the glass of the glasses). However one should not forget that the correction range is usually small, and in case of serious vision failures, the capabilities of the optics may not be enough; but such situations are still quite rare.