Mounts

A mount is a mechanical system that supports a telescope and allows direct it to any celestial object, and then to follow up. sivant models and types, it can either be attached to a tripod or be removable or either rest directly on the ground (see “dobson”). The quality of the mount and tripod is important because the addition of these two devices must ensure a stable base for the observation instrument, so that it does not vibrate by a blow or when there is wind. this robustness is particularly crucial for astrophotography which requires perfect image stability, sometimes for long periods. The mount should also be adapted to the weight and the amplitude of the instrument. A compact telescope requires a compact frame and vice versa.

Altazimuth Mount

This is the simplest and most intuitive mount. It has two perpendicular axes of rotation that can point the lens in all directions of the sky :

► The azimuth axis (AZ), which is a vertical axis to a left/right movement through 360 °.
► The altitude axis (ALT), which is a horizontal axis providing high/low movement of 90 °.

Most camera tripods, mounts binoculars or small telescopes initiation are of this type. The telescope can be referred to a base, maintained by a branch, it is quite light, or by two symmetrical branches. This is called “fork” mount.

Advantages
1. Easy to use, intuitive, requires no prior adjustment, no station layout (if not motorized). we can begin to observe when the instrument is installed.
2. No door overhang.
3. Low price due to the simplicity of its design.
4. Low maintenance.
5. Often lighter than the equatorial mount and therefore more easily transportable

Disadvantages
1. Without motorization, it is not suitable for prolonged observations or magnification because it requires two simultaneous movements in altitude and azimuth to keep an object in view. Indeed, the stars do not follow the up/down paths or left/right, but appear in a circle around the celestial pole. Therefore always catch the target by performing alternative monitoring azimuth and height (in steps), it is not convenient.
2. It may be impossible to target a nearby object zenith. This may be due to the length of the telescope, when trying to rotate it to 90 just banging on the frame, or at the very design of the frame. Consequently, then there will a blind spot that prevents from approaching the zenith. This is unfortunate since it is precisely here that the atmosphere in the least intrusive images.

DOBSON

The dobsonian mount is actually a simplified azimuthal mount placed on a “rocker”, that is to say, a rotating platform. Not needing a tripod, it is placed on the floor. It can be mounted on equatorial platform, in order to have the same property that equatorial mount.

The dobson name is now commonly used to describe a type of telescope as a whole (+ mount tube). In fact the word dobson in the strict sense only defines the frame on which is often placed an optical tube type newton. So it happens regularly that the novice is disturbed by the categories of telescopes presented on retail sites: one often find a section “newton” (which has optical formula newton telescopes on equatorial mounts), and – independent of celle- above – a heading “dobson” (which has optical formula newton telescopes on dobsonian mounts). This is not the optical configuration that changes here, as one might a priori to believe, but the mount type.

>> The simplicity is in the same time the main advantage and the main limitation of a Dobson.

Advantages
1. Allows you to aim an object overhead.
2. Very efficient hardware, so volume and weight.
3. Space-saving.
4. Cheap.

Disadvantages
1. The same discussed above for the azimuthal mount.

See Alt-azimuth mounts without GoTo on Astroshop.eu >>

Equatorial Mount

This mount is designed to synchronize the movement of the telescope with that of the observed object in order to keep performing one movement. They are available in manual or motorized version. The equatorial mounts have four components :

► The azimuth axis (AZ) That guides the telescope to the north if you are in the northern hemisphere, and vice versa.
► The altitude axis (ALT) which compensates for the latitude of the observation. It is graduated from 0 to 90 °. for example, if you are in a place 60 ° latitude it will lift the 60 ° telescope in order to put in parallel to the polar axis.
► The right ascension axis (AD) (or polar or zone) that is put in parallel with the axis of rotation of the earth and pointing towards one of the two celestial poles, according to which hemisphere you are in. it is he who will allow to follow the observed object. he graduated in 24 hours that correspond to the 24 celestial meridians.
► The axis of declination (DEC) That seeks the observed object. it is measured in 4 times 90 ° corresponding to 2 celestial hemisphere (180 ° + 180 °).

It is therefore an azimuthal mount (right ascension and declination axes) mounted on another azimuthal mount (azimuth and elevation axes), called equatorial table. The latter serves only to tilt the upper frame to be able to parallel its right ascension axis (AD) with the axis of rotation of the earth. As the distance between the two axes is extremely low compared to that separating the observer from the celestial object, we can consider that they are confused. once the object pointed by the axis of declination (DEC), simply rotate the telescope around the right ascension axis (AD) to compensate for the apparent motion of the sky, and thus keep the target middle of the eyepiece.
Advantages
1. Monitoring of the object observed with a single motion.
2. A single motorized shaft so enough to do astrophotography with long exposure time and without field derotator.
3. No blind spot.
4. Suitable for all types of instruments.

Disadvantages
1. Heavier than the azimuthal mount because of the counterweight, thus more difficult to transport.
2. Cantilever detrimental to the stability of the whole, especially with large telescopes.
3. More time consuming to station azimuth mount.
4. More expensive than the azimuthal mounts.

GERMAN MOUNT

This is the most common type of equatorial mount. The main piece is t-shaped and is composed of a pivot whose axis of rotation shall coincide with the polar axis, and a bar which corresponds to the axis of the variations, and on which there are counterweights which balance the structure where the telescope is tilted to the side. German mounts are suitable for all types of instruments.

If there is a celestial object in a low position in relation to the celestial pole, the telescope will strike the frame. Overnight observation, it is important to predict future positions of the tube, especially in the context of the practice of astrophotography sometimes requires several hours of time poses. It sometimes, being observed, perform a reversal of this axis in a symmetrical position, which is quite tricky.

FORK MOUNT

The equatorial fork mount is a azimuthal fork mount on an equatorial table. The azimuth axis is then inclined to be confused with the polar axis. This frame is less used than the german mount because it is much more cumbersome and causes important to overhang that makes it unusable with heavy instruments. In addition, its fork can receive a tube of a diameter greater than its width. Its big advantage is its strength.

HORSESHOE MOUNT

More rare, it is composed of a metal part shaped “horseshoe” based on a track that allows you to rotate the telescope around the right ascension axis. It does not have any tripod. this mount does not create an awkward ports (so no counterweight), is very stable, solid and precise. However, it is only suitable as newtonian telescope and eyepiece can be difficult to access in certain positions.