Mount and tripod
Increasingly, motorized mounts are being used for astrophotography in order to follow the objects moving along the sky as accurately as possible due to the Earth's rotation. Two types of mounts are available, the azimuthal mount (often installed in a fork mount) and the equatorial mount.
azimuthal fork mount
The advantage of an azimuthal mount is the easy handling when setting up and observing the sky with eyepieces. The disadvantage of an azimuthal mount with motorized tracking is that the field of view is rotated by the earth's rotation, since the mount can only move horizontally and vertically to the set-up plane.
Azimuthal and equatorial mount tracking [https://www.privatsternwarte.net] (translated)
Comparison of image field rotation between azimuthal and parallactic mounts [Baader Planetarium GmbH] (translated)
Equatorial mounts are used when it is intended to work with long exposure times. Compared to an azimuthal mount, they have the advantage that they can exactly follow celestial objects along their earth rotation. This is done by rotating a right ascension or hour axis parallel to the Earth's rotation axis.
Since generally only the equatorial mount is suitable for astrophotography, only this mount will be considered in the following.
The main assembly of a parallactic mount is the central part, the axis cross, in which the two important tracking axes are perpendicular to each other, and the polar finder is attached.
Equatorial mount with representation of the components
Equatorial mount with display of the axes
Source of image for Equatorial mount: [www.teleskop-express.de]
The right ascension axis can be used to track celestial objects at the speed of the Earth's rotation in an East-West direction.
By means of the declination axis the distance of the celestial objects to the celestial equator (Earth's rotation plane) is set.
Via the polar finder aligned with the right ascension axis, this axis can be aligned parallel to the Earth's rotation axis.
Terms related to the celestial sphere
Celestial sphere with representation of angles
At the upper end of the axis cross there is a rail on which the telescope tube is mounted. A counterweight is mounted opposite the tube in order not to place too much stress on the bearings of the right ascension axis.
Below the two tracking axes is a construction with two further axes, via which the mount is attached to a tripod or on a column. With the pole height axis, the inclination (corresponding to the latitude) of the telescope can be adjusted, and with the help of the azimuth screws, the deviation from the meridian is minimized.
Even if a high payload is specified for the mounts in the data sheets, this only applies if the night sky is viewed with the eyepiece. According to an often confirmed rule of thumb, which is listed in many forum contributions, the telescope tube with the complete accessories (camera, guider, eyepiece focuser. etc.) should not weigh more than 50% - 65% of the specified payload. (Note: The counterweights are not added in this calculation.) The reason is simple. The smallest shocks and vibrations will be directly visible on the long-exposure capturing. Additionally, large tubes have a center of gravity further out, which implies even better stability. The mount should therefore be operated far from its maximum payload.
The same applies to the tripod on which the whole construct stands. The tripod should be as stable as possible. It should be able to absorb oscillations well, so that vibrations are not passed on to the telescope.