Comparison Celestron AstroMaster 80AZS vs Celestron Travel Scope 80

The highest resolution magnification that a telescope can provide. In fact, this is the magnification at which the telescope provides maximum detail of the image and allows you to see all the small details that, in principle, it is possible to see in it. When the magnification is reduced below this value, the size of visible details decreases, which impairs their visibility, when magnified, diffraction phenomena become noticeable, due to which the details begin to blur.

The maximum resolving magnification is less than the maximum useful one (see above) — it is somewhere around 1.4 ... 1.5 of the lens diameter in millimetres (different formulas give different values, it is impossible to determine this value unambiguously, since much depends on the subjective sensations of the observer and features of his vision). However, it is worth working with this magnification if you want to consider the maximum amount of detail — for example, irregularities on the surface of the Moon or binary stars. It makes sense to take a larger magnification (within the maximum useful one) only for viewing bright contrasting objects, and also if the observer has vision problems.

The type of finder provided in the design of the telescope.

A seeker is a device designed to point the device at a specific celestial object. The need for such a device is due to the fact that telescopes, due to the high magnification, have very small viewing angles, which greatly complicates visual guidance: such a small area of \u200b\u200bthe sky is visible in the eyepiece that it is possible to determine from these data exactly where the telescope is pointed and where it needs to be turning around is almost impossible. Pointing "on the tube" is very inaccurate, especially in the case of mirror models that have a large thickness and relatively short length. The seeker, on the other hand, has a low magnification (or works without magnification at all) and, accordingly, wide viewing angles, thus playing the role of a kind of “sight” for the main optical system of the telescope.

The following types of finders can be used in modern telescopes:

— Optical. Most often, such finders look like a small monocular directed parallel to the optical axis of the telescope. In the field of view of the monocular, markings are usually applied, showing which point in the visible space corresponds to the field of view of the telescope itself. In most cases, optical finders also provide a certain magnification — usually on the order of 5 – 8x, so when working with such systems, usually, the initial pointing of the telescope "...on the tube" is still required. The advantages of optics, as compared to LED finders, are the simplicity of design, low cost, and good suitability for observations in the city, suburbs, and other conditions with fairly bright skies. In addition, such devices do not depend on power sources. Against the background of a dark sky, the markings may be poorly visible, but for such cases there is a specific kind of finders — with an illuminated crosshair. However the backlight requires batteries, but even in the absence of them, the markings remain visible — as in a conventional, non-illuminated finder. Devices of this type are indicated by an index traditional for optics of two numbers, the first of which corresponds to the multiplicity, the second to the diameter of the lens — for example, 5x24.

— With point guidance (LED). This type of seekers is similar in principle to collimator sights: an obligatory design element is a viewing window (in the form of a characteristic glass in a frame), onto which a mark is projected from a light source. This mark can look like a dot or another shape — crosshairs, rings with a dot, etc. The device of such a finder is such that the position of the mark in the window depends on the position of the observer's eye, but this mark always points to the point at which the telescope is pointed. LED finders are more convenient than optical ones in the sense that the user does not have to bring the eye close to the eyepiece — the mark is well visible at a distance of 20 – 30 cm, which makes it easier to point in some situations (for example, if the observed object is located close to the zenith). In addition, such devices are great for working with dark skies. They usually do not have magnification, but this cannot be called a clear disadvantage — for a seeker, a wide field of view is often more important than zoom. But from the unambiguous practical shortcomings, it is worth noting the need for a power source (usually batteries) — without them, the system turns into a useless piece of glass. In addition, collimators as a whole are noticeably more expensive than classical optics, and the mark may be lost against the background of an illuminated sky.

Note that there are telescopes that do not have seekers at all — these are models with a small objective diameter, in which the minimum magnification (see above) is small and provides a fairly wide field of view.

The presence of an antireflection coating on the surface of the lenses, and sometimes also the prisms of the telescope. Such a coating creates characteristic coloured reflections or iridescent stains on the glass surface.

The meaning of enlightenment is clear from the name: this feature improves the overall light transmission, thus providing a brighter, clearer and higher quality image. For telescopes, this is especially important, since such instruments are used mainly at night and deal with very little light. The general principle behind AR coatings is that they reduce the reflectance of a lens/prism, allowing more light to pass through. In fact, this is implemented as follows: light passes through the coating to the main glass, is reflected from it, but instead of being scattered, it reaches the boundary between the coating and air and is already reflected from it, turning “back” in the original direction. Similarly, it is possible to reduce light loss by reflection from 5% (uncoated lens) to 1% with single-coated and 0.2% or even less with multi-coated; at the same time, due to the microscopic thickness, such coatings do not introduce geometric distortions in the visible image.

Usually, the type of enlightenment is additionally specified in the manufacturer's documentation, and sometimes directly in the characteristics. There are 4 main types in total, here are their main features:

— Single layer (C). One layer of coating on individ...ual (not all) optical elements, and most often only on the outer surface of the lens. This is the simplest and most inexpensive option, used mainly in inexpensive models that are not designed for serious tasks. This is due to the fact that, in general, single-layer enlightenment acts only on a part of the visible spectrum, which is why it is inferior to a multi-layer coating both in terms of efficiency and colour fidelity (sometimes colour distortions can be quite noticeable). And in this case, such a coating is also not applied to everything, but only to individual parts of the optical system. So although single-layer enlightenment is better than none at all, it is suitable mainly for entertainment applications.

— Full single layer (FC). Single-layer coating applied to all optical elements of the telescope. It gives the maximum efficiency available for such coatings in principle. However, since this type of coating is effective only for a relatively small part of the visible spectrum, the quality of colour reproduction is still lower than in multilayer systems.

— Multilayer (MC). Coating of several layers with different refractive indices applied to one or more optical elements (but not all). The number of layers can be different — from 2 – 3 in relatively inexpensive solutions to 6 – 8 or more in high-end telescopes. However, even relatively simple multilayer coatings cover almost the entire visible spectrum and are several times superior to single-layer coatings in terms of reflection reduction. So if good brightness and reliable colour reproduction are important to you, then this option will be more preferable than even full single-layer enlightenment, not to mention incomplete. On the other hand, such optics are more expensive than solutions with a single layer of antireflection coating.

— Full multilayer. The most advanced type of coating: a multi-layer coating applied to all elements of the optical system. This option provides extremely high light transmission and true colour reproduction, but it comes at a cost. Therefore, it can be found mainly among high-end telescopes; and it’s worth looking specifically for a model with such enlightenment when both the brightness of the picture and the reliability of colours are of fundamental importance to you.

The presence of a diagonal mirror in the design or scope of delivery of the telescope.

This accessory is used in combination with lens and mirror-lens telescopes (see "Design"). In such models, the eyepiece is located at the end of the tube and is directed along the optical axis of the telescope; in some situations — for example, when observing objects near the zenith — such an arrangement can be very inconvenient for the observer. The diagonal mirror allows you to direct the eyepiece at an angle to the optical axis, which provides comfort in the situations mentioned. However the image usually turns out to be mirrored (from right to left), however, when observing astronomical objects, this can hardly be called a serious drawback. Diagonal mirrors can be both removable and built-in, it can also be possible to change the angle of rotation of the eyepiece.

A device that allows you to install a smartphone on a telescope so that the camera of the device “sees” the image in the eyepiece. Thus, you can take photos and videos on your smartphone, as well as use its screen as an eyepiece — for example, if you want to show the image to several people at once.

The total weight of the telescope assembly includes the mount and tripod.

Light weight is convenient primarily for "marching" use and frequent movements from place to place. However, the downside of this is modest performance, high cost, and sometimes both. In addition, a lighter stand smooths out shocks and vibrations worse, which may be important in some situations (for example, if the device is installed near a railway where freight trains often pass).