Comparison Celestron AstroMaster 130 EQ vs Arsenal 130/650 EQ2

The type of mount the telescope is equipped with.

A mount is a mechanical unit with which the telescope is attached to a tripod or (in some cases) installed directly on the ground. In addition to mounting, this unit is also responsible for pointing the optics at a certain point in the sky. The most popular nowadays are azimuth devices in different variations - AZ1, AZ2, AZ3, as well as in the form of the so-called Dobson mount. Equatorial mechanisms of different models ( EQ1, EQ2, EQ3, EQ4, EQ5) are noticeably more complex and more expensive, but they provide more possibilities. There are systems that combine both of these types of mounts at once - the so-called azimuth-equatorial ones. And finally, some telescopes are supplied without a mount at all. Here's a more detailed description of these options:

- Azimuthal. The full name is “alt-azimuth”. Traditionally, it has two axes of rotation of the telescope - one for pointing in altitude, the second in azimuth. Different models of such mounts differ in additional control capabilities:

• AZ1. They d...o not have a precision movement system.
• AZ2. Equipped with a system of precise vertical movement (around the horizontal axis).
• AZ3. Equipped with precision movement systems on both axes.

In any case, the second axis (azimuthal) in such systems is always located vertically, regardless of the geographical location of the telescope; This is the key difference from the equatorial mounts described below. In general, azimuth mechanisms are quite simple and inexpensive in themselves, while being quite convenient and practical, which is why this option is the most popular in our time. In addition, they are ideal for observing ground objects. The key disadvantage of this option is its poor suitability for continuous “accompaniment” of celestial bodies (moving across the sky due to the rotation of the Earth). If in a correctly configured equatorial mechanism you need to rotate the telescope along only one axis, then in the azimuthal mechanism you need to use both axes, and unevenly. The situation can be solved using an auto-tracking system, but this function significantly affects the price of the entire device. And even its presence does not guarantee that the telescope is suitable for astrophotography at long exposures - after all, with such use it is necessary to ensure not only accurate movement along each individual axis, but also correction for image rotation in the frame (which is not provided in every auto-tracking system, and also increases the price more).

- Dobson. A specific variation of the alt-azimuth mounts described above, used almost exclusively in reflectors. It also provides two axes of rotation - horizontal and vertical. The key feature of the Dobsonian mount is that it is not designed for a tripod and is mounted directly on the ground or other flat surface; For this purpose, the design provides a wide, massive base. Such systems are excellent for Newtonian telescopes, in which the eyepiece is located in the front part: thanks to the low position of the tube on the mount, the eyepiece itself is at a fairly convenient height. Also, the advantages of “Dobsons” include simplicity, low cost and at the same time good reliability, making them suitable even for large and heavy telescopes. Among the disadvantages, we should note the poor compatibility with uneven surfaces, especially hard ones, like solid rock (while tripods used with other types of mounts do not have this disadvantage).

- Equatorial. Mounts of this type make it possible to synchronize the movement of the telescope with the movement of celestial bodies across the sky, resulting from the rotation of the Earth. The conventional vertical axis, responsible for rotating the telescope from side to side, in such mechanisms is called the right ascension axis (RA), and the horizontal (for pointing along the conventional vertical) is called the declination axis (Dec.). Before use, the equatorial mount is adjusted so that the right ascension axis is directed to the “celestial pole”, parallel to the axis of rotation of the Earth (“the celestial axis”); the specific inclination relative to the vertical depends on the geographic latitude of the observation site. This format of work significantly complicates both the design of the mount itself and the installation procedure. On the other hand, equatorial systems are ideal for long-term “accompaniment” of astronomical objects: in order to compensate for the movement of a celestial body due to the rotation of the Earth and keep the target in the field of view, it is enough to rotate the telescope around the RA axis to the right (clockwise), and with a clearly defined speed - 15° per hour, regardless of the vertical position of the object. This makes such designs ideal for astrophotography, including deep space objects that require long exposures. In fact, this does not even require a full-fledged auto-tracking system - a relatively simple clock mechanism that rotates the telescope around the right ascension axis is enough. The downside of these advantages, in addition to the mentioned complexity and high cost, is their poor suitability for large, heavy telescopes - as the weight of the instrument increases, the weight of a suitable equatorial system increases even faster.
As for the different models of such mounts, they are marked with an alphanumeric index, from EQ1 to EQ5. In general, the higher the number in the designation, the larger and heavier the structure itself (including the tripod, if supplied), the less suitable it is for moving from place to place, but the better it dampens vibrations and shocks. But the restrictions on the weight of the telescope are not directly related to the equatorial mount model.

— Azimuthally-equatorial. Mechanisms that combine two types of mounts. It looks like this: an azimuthal system is installed on a tripod, and an equatorial system is installed on it, in which the telescope is already mounted. This design allows you to use the capabilities of both types of mounts. Thus, the azimuthal mechanism is quite suitable for observing large celestial bodies in near space (the Moon, planets) and large areas of the sky (such as constellations), and it does not require complex preliminary settings. And for astrophotography or for viewing deep space objects at high magnifications, it is more convenient to use the equatorial system. However, in practice, such versatility is extremely rarely required, despite the fact that the combination of two types of mounts complicates the design, increases its cost and reduces reliability. So this option can be found in single models of telescopes.

- Without a mount. The complete absence of a mounting system in the kit does not allow using the telescope out of the box. However, it can be the best option in some cases. The first is if the customer wants to choose the mount at his own discretion, without relying on the manufacturer's decision, or even assemble it himself (for example, quite a lot of astronomers make their own Dobsonian systems). The second typical case is if the household already has a mount (for example, from an old telescope that has fallen into disrepair), and there is simply no need to overpay for a second one. In any case, when choosing such a model, you should pay special attention to the type of fastening for which the pipe is designed - compatibility with a specific mount directly depends on it.

The resolution of the telescope, determined according to the Dawes criterion. This indicator is also called the Dawes limit. (There is also a reading of "Daves", but it is not correct).

Resolution in this case is an indicator that characterizes the ability of a telescope to distinguish individual light sources located at a close distance, in other words, the ability to see them as separate objects. This indicator is measured in arc seconds (1 '' is 1/3600 of a degree). At distances smaller than the resolution, these sources (for example, double stars) will merge into a continuous spot. Thus, the lower the numbers in this paragraph, the higher the resolution, the better the telescope is suitable for looking at closely spaced objects. However, note that in this case we are not talking about the ability to see objects completely separate from each other, but only about the ability to identify two light sources in an elongated light spot that have merged (for the observer) into one. In order for an observer to see two separate sources, the distance between them must be approximately twice the claimed resolution.

According to the Dawes criterion, the resolution directly depends on the diameter of the telescope lens (see above): the larger the aperture, the smaller the angle between separately visible objects can be and the higher the resolution. In general, this indicator is similar to the Rayleigh criterion (see "Resolution (Rayleigh)"), however, i...t was derived experimentally, and not theoretically. Therefore, on the one hand, the Dawes limit more accurately describes the practical capabilities of the telescope, on the other hand, the correspondence to these capabilities largely depends on the subjective characteristics of the observer. Simply put, a person without experience in observing double objects, or having vision problems, may simply “not recognize” two light sources in an elongated spot if they are located at a distance comparable to the Dawes limit. For more on the difference between the criteria, see "Resolution (Rayleigh)".

The resolution of the telescope, determined according to the Rayleigh criterion.

Resolution in this case is an indicator that characterizes the ability of a telescope to distinguish individual light sources located at a close distance, in other words, the ability to see them as separate objects. This indicator is measured in arc seconds (1 '' is 1/3600 of a degree). At distances smaller than the resolution, these sources (for example, double stars) will merge into a continuous spot. Thus, the lower the numbers in this paragraph, the higher the resolution, the better the telescope is suitable for looking at closely spaced objects. However, note that in this case we are not talking about the ability to see objects completely separate from each other, but only about the ability to identify two light sources in an elongated light spot that have merged (for the observer) into one. In order for an observer to see two separate sources, the distance between them must be approximately twice the claimed resolution.

The Rayleigh criterion is a theoretical value and is calculated using rather complex formulas that take into account, in addition to the diameter of the telescope lens (see above), the wavelength of the observed light, the distance between objects and to the observer, etc. Separately visible, according to this method, are objects located at a greater distance from each other than for the Dawes limit described above; therefore, for the same tel...escope, the Rayleigh resolution will be lower than that of Dawes (and the numbers indicated in this paragraph are correspondingly larger). On the other hand, this indicator depends less on the personal characteristics of the user: even inexperienced observers can distinguish objects at a distance corresponding to the Rayleigh criterion.

This item indicates the eyepieces included in the standard scope of delivery of the telescope, or rather, the focal lengths of these eyepieces.

Having these data and knowing the focal length of the telescope (see above), it is possible to determine the magnifications that the device can produce out of the box. For a telescope without Barlow lenses (see below) and other additional elements of a similar purpose, the magnification will be equal to the focal length of the objective divided by the focal length of the eyepiece. For example, a 1000 mm optic equipped with 5 and 10 mm "eyes" will be able to give magnifications of 1000/5=200x and 1000/10=100x.

In the absence of a suitable eyepiece in the kit, it can usually be purchased separately.

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 type of mirror installed in a reflector or combined model (see “Design”).

Let us recall that the mirror in such models performs the same function as the objective lens in classical refracting telescopes - that is, it is directly responsible for magnifying the image. The type of mirror is indicated by its general shape:

- Spherical. The most common option, which is primarily due to ease of production and, as a consequence, low cost. On the other hand, a spherical mirror, purely technically, is not capable of concentrating a beam of light as effectively as a parabolic one does. This causes distortions known as spherical aberrations; they can lead to a noticeable deterioration in sharpness, and this effect becomes most noticeable at high magnifications. True, there are telescopes that are practically not susceptible to this phenomenon - namely, long-focus models in which the focal length is 8 to 10 times the size of the mirror; however, such devices are bulky and heavy. In light of this, it is worth specifically looking for models with this type of mirrors mainly in two cases: either if the telescope is planned to be used at a relatively small magnification (for example, for observing the Moon, planets, constellations), or if you are not bothered by the dimensions and weight.

— Parabolic. Mirrors in the shape of a paraboloid of rotation almost perfectly concentrate the rays entering the telescope at the desi...red point in the optical system. Thanks to this, reflectors with such equipment provide a very clear image even at high magnification levels and regardless of the focal length. The main disadvantage of this type of mirror is the rather high cost associated with the complexity of production. So it makes sense to pay attention to parabolic reflectors primarily when the described advantages clearly outweigh; A typical example is the search for a relatively compact telescope for observing deep space objects.

The ability to install a camera allows you to use the telescope for astrophotography without making additional changes to the design.

To mount the camera in telescopes, a standard “T-mount” threaded connection is usually provided (more precisely, “T2 mount”: the original “T” type mount is smaller, but almost never occurs nowadays). This connection allows you to install not only specialized "astronomical" cameras, but also conventional cameras with interchangeable lenses (reflex and "mirrorless"). However a modern digital camera will need an adapter, since initially such models use other types of lens mounts; however, finding such an adapter is usually not a problem. And some outdated devices (mostly film ones) initially use T2-mount and can be installed directly, without an adapter.

We also recall that astrophotography often involves long exposures, and for such conditions, the best option would be an equatorial mount system (see "Mounting").

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).