Comparison Nikon Action EX 10x50 CF WP vs Celestron Granite ED 10x50

The angle of view provided by binoculars/monoculars and available to the eye of the observer. This parameter can be described as the angle between the lines connecting the two extreme points of the image visible in the eyepiece with the eye of the observer; in other words, this is the sector actually observed through binoculars (as opposed to the actual angular field of view described below). The greater the value of this parameter, the greater part of the observed space can be seen without turning the instrument. On the other hand, a wide field of view reduces the magnification factor (see above) — or significantly increases the cost of the device compared to more focused ones.

The smallest distance to the observed object, at which it will be clearly visible through binoculars / monoculars. All such optical instruments were initially created for observing remote objects, therefore, not all of them are able to work at short distances. When choosing a model for this parameter, one should proceed from the expected observation conditions: ideally, the minimum focus distance should not be greater than the smallest possible distance to the observed object.

The presence of a phase correction system in binoculars / monoculars. This feature enhances image quality, such as resolution and colour reproduction, and minimizes colour distortion. The need to use phase correction is due to the fact that the light waves corresponding to different colours differ in length and penetrating power, which is why they also pass through the optical system in different ways. This may cause image quality degradation. To avoid this, special coatings are used in the prisms installed in the device — they retain the original ratio of colour waves and thus provide phase correction.

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 binoculars / monoculars are planned to be used simultaneously with glasses — because in such cases it is not possible to bring the eyepiece close to the eye.

Coating is a special coating applied to the surface of the lens. This coating is intended to reduce light loss at the air-glass interface. Such losses inevitably arise due to the reflection of light, and the antireflective coating “turns” the reflected rays back, thus increasing the light transmission of the lens. In addition, this function reduces the amount of glare on objects visible through binoculars/monoculars. There are single-layer, full single-layer, multi-layer, full multi-layer. More details about them:

- Single layer. This marking indicates that one or more lens surfaces (but not all) have a single layer of anti-reflective coating applied to them. This is inexpensive and can be used even in entry-level optical instruments. On the other hand, it filters out a certain spectrum of light, which distorts the color rendition in the visible image - sometimes quite noticeably. In addition, in this case, on some lens surfaces there is no coating at all, which inevitably leads to glare in the field of view. Thus, single-layer coating is the simplest type and is used extremely rarely, mainly in budget models.

- Full single layer. A variation of the single-layer coating described above, in which an anti-reflective coating is present on all surfaces of the lenses (at each air-glass interface). Although this option is al...so characterized by color distortion, it is devoid of another, the most key drawback of “incomplete” enlightenment - glare in the field of view. And the mentioned color distortion is most often not critical. With all this, full single-layer coating is relatively inexpensive, which is why it is very popular in entry-level and entry-mid-level models.

- Multi-layered. A type of coating in which multiple layers of reflective coating are applied to one or more lens surfaces (but not all). The advantage of such a coating over a single-layer coating is that it uniformly transmits almost the entire visible spectrum and does not create noticeable color distortions. The absence of a coating on individual surfaces reduces the cost of the device (compared to full multi-layer coating), but it is impossible to completely get rid of glare in such a system.

- Fully multi-layered. The most advanced and effective of modern types of coating: a multilayer coating is applied to all surfaces of the lenses. This way, high brightness and clarity of the “picture” is achieved, with natural color rendition and no glare. The classic disadvantage of this option is its high cost; Accordingly, full multi-layer coating is typical mainly for high-end models.

A type of prism used in binocular/monocular construction. A prism is one of the key elements of an optical system: it is a glass polyhedron through which light passes on its way from the lens to the eyepiece. The need to use such polyhedra is associated with the peculiarities of the creation of optical devices of high multiplicity. In other models, there are two main options:

— Porro. A distinctive feature of binoculars with such prisms is that the optical axes of the eyepieces are offset relative to the lenses — in other words, the distance between the eyepieces differs from the distance between the output lenses. This makes the design somewhat more cumbersome than with Roof prisms; on the other hand, the lenses can be spread over a long distance, which provides a better sense of the volume of the observed picture — especially at long distances. In addition, binoculars with Porro prisms are easier to equip with interpupillary distance adjustment (see below).

— Roof. In models with prisms of this type, the eyepiece and the objective are on the same optical axis — the binoculars look as if the light in it goes from "input" to "exit" directly, without any prism at all (although in reality this, of course, is not So). Such devices are smaller and lighter than Porro systems, but more complex and more expensive.

Material used for prisms found in binoculars and monoculars.

- BK-7. A type of borosilicate optical glass (6LR61), a relatively inexpensive and at the same time quite functional material that provides, although not outstanding, quite acceptable image quality. Used in entry-level and mid-level models.

—BaK-4. Barium optical glass, noticeably superior to BK7 in brightness and image clarity, is however also more expensive. Accordingly, it is found mainly in the premium segment.

The presence in the design of the optical device of lenses made of low-dispersion glass: ED (Extra-low Dispersion), LD (Low Dispersion), SLD (Special-low Dispersion), ELD (Extraordinary-low Dispersion), UL (Ultra-low Dispersion), etc. P.

Such elements in the optical design are responsible for minimizing the level of dispersion - this phenomenon is characterized by the “stratification” of the light stream after refraction, since different parts of the spectrum are refracted at different angles. Delamination entails a loss of image clarity and provokes the appearance of chromatic aberrations - colored borders at the boundaries of high-contrast transitions along the edges of individual objects. Low dispersion glass ensures the refraction of all light waves at the same angle, thereby minimizing chromatic distortion and improving color rendering and resolution parameters. At the same time, the use of such glass significantly affects the cost of the optical device, so low-dispersion glass often remains the prerogative of high-end models.

Interpupillary distance adjustment range provided in binoculars with the corresponding function.

Recall that, ideally, the interpupillary distance of the device should correspond to the distance between the centers of the pupils of the user himself. With this calculation, it is worth choosing binoculars according to this parameter; and if the device will be used by several people, it is worth making sure that they all “fit” into the adjustment range of the selected model. However, not every person knows exactly their interpupillary distance, especially since it changes with age; and the circle of users can be indefinite — for example, if we are talking about "rolling" binoculars in the hunting industry. In such cases, it is worth proceeding from the following.

In adults of more or less standard physique, the interpupillary distance is in the range from 60 to 66 mm. Modern binoculars cover this range with a margin — even the most modest models support values from 60 to 70 mm, and in most cases the lower limit of the range lies in the region of 54 – 57 mm, and the upper one — 72 – 75 mm. This is quite enough for most adults, including those with a non-standard physique — miniature, or vice versa, large. So a wider range may come in handy only in special cases. For example, if a child will use binoculars, it is desirable that the lower adjustment limit be lower than the standard 50 – 55 mm (in some models, this limit is at the level of 38 mm, or even 34 mm).