Altazimuth mount
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An Altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; a horizontal (altitude) axis, and a vertical (azimuth) axis. They are generally used with telescopes, cameras, radio antennas, heliostatic mirrors, or solar panels.
[edit] Telescope altazimuth mounts
Altazimuth mounts are used in a range of telescope types from simple consumer level telescope mounts and home built amateur telescopes all the way up to very large research telescopes. The biggest advantage of alt-azimuth mounts is their simplicity of their mechanical design. The primary disadvantage of altazimuth mounts is that they cannot follow astronomical objects in the night sky as the Earth spins on its axis the way an equatorial mount can. Equatorial mounts only have to be moved on one axis of rotation at a constant rate to efficiently follow the rotation of the night sky (diurnal motion). Altazimuth mounts have to be moved in two axis at variable rates and they also impart a rotation to the field of view. They also do not allow for the use of setting circles to locate astronomical objects. The advent of microprocessor controlled systems has made it possible to compensate for all these variables and limitations imparted by altazimuth mounts, making them suitable for diurnal tracking, object photography and imaging, and precise object location and even automated object location.
[edit] Applications
Some of the applications altazimuth mounts are used in include:
- Research telescopes
- Mounts for very large telescopes. In the largest telescopes the mass and cost of an equatorial mount is prohibitive. The simple structure of an alt-azimuth mount is much better suited to such large heavy instruments.
- Amateur astronomical telescopes
- Beginner telescopes. Altazimuth mounts are used as simple to use low cost telescope mounts.
- Dobsonian style telescopes. Telescopes built on the very popular Dobsonian design employ a variant of the alt-azimuth mount due to its ease of construction and use. Dobsonian style telescopes are optimized for visual astronomy, and the alt-azimuth mount is more suitable for this larger class of instrument since it doesn't add the unnecessary mass, complexity, and expense of an equatorial mount.
- Goto telescopes. Altazimuth mounts offer telescope manufactures the ability to combine simplified mechanical design with modern electronics to make a more affordable and simple to use mounting system. In particular, it has often proved more convenient to build a simple alt-azimuth mount and use a computer to manipulate both axes to track an object, than to build a more mechanically complex equatorial mount that employs only a single motor. When astrophotography is involved, a further motor has to be used to rotate the camera to match the field of view for long exposure photographs.
