Comparison Celestron Ultima 100/45 vs Celestron Regal M2 100 ED

The magnification of the image provided by a telescope. Roughly speaking, this parameter describes how many times the object seen in the eyepiece of the pipe will be larger than when viewed from the same distance with the naked eye.

Multiplicity — the first number (numbers) in the digital marking of optical instruments: for example, the designation 25-75x50 corresponds to a multiplicity from 25x to 75x. Note that most modern telescopes have variable (adjustable) magnification. This allows you to choose the mode of operation depending on the situation: to search for the desired object, it is more convenient to reduce the magnification, providing a wide field of view, and having found it, increase the magnification and examine in detail. However in some models, to change the magnification, you need to replace the eyepiece (see "Replacement eyepiece").

High magnification, on the one hand, makes the tube "long-range" and makes it easy to examine small objects at considerable distances. On the other hand, the angle of view decreases in this case, which makes it difficult to observe moving objects and even aim the optics at the target. In addition, with an increase in the magnification, the diameter of the exit pupil also decreases (see below) and the aperture ratio of the tube; you can compensate for this moment by increasing the lens, but this accordingly affects the price. So it makes sense to specifically look for powerful optics with a high degree of ma...gnification only when such capabilities are fundamentally important.

The field of view of the telescope at a distance of 1 km to the objects under consideration, the so-called "linear field of view". In fact, this is the width (diameter) of the space that falls into the field of view when observed from a distance of 1 km.

This parameter is widely used in the characteristics of telescopes along with the angular field of view (see below): the linear field of view data is more visual and closer to practice, it allows you to evaluate the capabilities of a telescope without resorting to special calculations.

For models of variable magnification (the majority of them), the linear field of view is indicated in the form of two numbers — for the minimum and for the maximum magnification.

Angle of view provided by a telescope.

If you draw two lines from the centre of the lens to two opposite points along the edges of the field of view of the pipe, the angle between these lines will correspond to the angular field of view. Accordingly, the larger the angle, the wider the field of view; however, individual items in it will look smaller. Conversely, an increase in magnification is inevitably associated with a decrease in the viewing angle. And since most modern telescopes have a variable magnification, the angular field of view is also variable, and in the characteristics this indicator is indicated in the form of two numbers — for the minimum and for the maximum magnification.

The smallest distance to the object under consideration at which the telescope is able to fully focus on it — that is, the minimum distance at which the image in the eyepiece will remain clear.

Spotting scopes were originally designed for viewing distant objects, so focus problems can occur if the distance is too small. Thus, manufacturers indicate this parameter in the characteristics. However, even in the most powerful and "long-range" models, the minimum focus distance is about 25 m — at this distance, the naked eye is often enough. Therefore, you should pay attention to this parameter only in cases where the ability to work normally close is of fundamental importance — for example, if the pipe is used at a shooting range, where the distance to the targets can be different, including pretty small.

Removal of the exit pupil of a telescope.

About the exit pupil itself, see above. Here we note that the offset is such a distance from the eyepiece lens to the observer's eye, at which the size of the visible image from the lens corresponds to the visible size of the eyepiece lens. In other words, the observed "image" in this case occupies the entire space of the eyepiece, without vignetting (darkening at the edges) and without "spreading" beyond the edges of the eyepiece. In this case, the overall image quality will be the best.

When looking down the pipe with the naked eye, the observer usually has no problem getting into the offset distance, and this parameter can be ignored. Problems can arise if the user wears glasses and the diopter adjustment (see above) is not sufficient to comfortably view without glasses. In such cases, it is desirable to use models with eye relief of at least 15 mm: although such a distance will not provide the highest image quality when viewed with glasses, it will allow using the device without any special difficulties. However, in modern telescopes, this parameter can reach 18 mm or even more.

Also note that eye relief may decrease somewhat with increasing magnification; in such cases, two numbers are indicated in the characteristics, corresponding to the removal at the minimum and at the maximum magnification.

The type of optics enlightenment provided in the telescope.

Enlightenment is called a special coating applied to the surface of the lens. This coating is designed to reduce light loss at the air-glass interface. Such losses inevitably arise due to the reflection of light, and the anti-reflective 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 a telescope.

Enlightenment types can be:

— Single layer. This marking means that one or more surfaces of the lenses (but not all) have been coated with a single layer of anti-reflection coating. This is inexpensive and can be used even in entry-level optical devices. On the other hand, it filters out a certain spectrum of light, which distorts the colour reproduction in the visible image — sometimes quite noticeably. In addition, in this case, on some surfaces of the lenses there is no coating at all, which inevitably leads to the appearance of glare in the field of view. Thus, single-layer enlightenment is the simplest variety and is used extremely rarely, mainly in low-cost models.

— Full single layer. A variation of the single-layer coating described above, in which an anti-reflection coating is present on all lens surfaces (at each air-glass interface). Although this option is also characterized...by colour distortion, it is devoid of another, the most key drawback of “incomplete” enlightenments — glare in the field of view. And the mentioned colour rendition distortion is most often not critical. With all this, full single-layer enlightenment is relatively inexpensive, due to which it is very popular in spyglasses of primary and primary-intermediate levels.

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

— Full multilayer. The most advanced and effective of today's types of coating: a multi-layer coating is applied to all lens surfaces. Thus, high brightness and clarity of the “picture” are achieved, with natural colour reproduction and the absence of glare. The disadvantage of this classic option is the high cost; accordingly, full multilayer enlightenment is typical mainly for high-end telescopes.

Spyglasses, originally intended for digiscoping — taking photographs through the eyepiece of an optical device. In this case, the tube plays the role of a super long-focus lens, providing magnifications that are not available for traditional telephoto lenses.

With certain tricks, almost any telescope can be used for such shooting (the first digiscopers generally held the cameras in front of the eyepiece with their hands). However, it is most convenient to use devices that were originally designed for this application. Usually, the marking “for digiscoping” means at least the presence of adapters for installing digital cameras in the kit. At the same time, such adapters can have a different design and purpose. So, some are designed for compact digital cameras that shoot directly through the eyepiece, and allow you to quickly bring the camera to the "pupil" and remove it for further observation in the usual way. Others are designed to mount a SLR or mirrorless camera, when a telescope, in fact, is installed instead of a lens, and the screen or camera viewfinder plays the role of an eyepiece. Features of complete adapters and other specialized functions should be specified separately.

The presence of a swivel body in the design of the telescope.

This term usually means the ability to rotate the back of the device, with the eyepiece, relative to the lens. This feature is found mainly in models with a 45° eyepiece (see “Eyepiece position”), as well as in “straight” tubes with Porro prisms, in which the eyepiece axis is offset relative to the lens axis. In both cases, the swivel body allows you to choose the most advantageous position of the lens, depending on the situation. For example, for observations of the sky, it is most convenient to hold a curved body in a standard position, with the eyepiece up; and by turning the “peephole” down, you can conveniently observe wildlife from a pit or other shelter, hiding in it entirely and exposing only the pipe lens to the outside. Similarly, turning a straight eyepiece can be useful to adjust the scope to the situation.

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 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.