Large Zenith Telescope

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The Large Zenith Telescope ( LZT ) is a reflecting telescope with a 6 m diameter, which is focused exclusively on the zenith due to the used primary mirror of liquid mercury: a zenith telescope. Its location is in the Malcolm Knapp Research Forest, University of British Columbia, approximately 70 kilometers east of Vancouver.

Liquid mirror

The primary mirror of the LZT consists of liquid mercury. This is in a uniformly rotating shell so that it receives a nearly perfect parabolic shape by interaction of centrifugal force and gravity.

For a vibrationaproof rotation, the shell is done with an air bearing; a drive via a built- in air bearing brushless electric motor. The rotation speed is in this case detected by an optical encoder, and is kept constant by a control loop. To keep the influence of air currents from the mercury surface of the mirror is covered with a thin mylar film.

Properties

The advantage of this concept are omitted, the low cost, the elaborate production of the mirror and its mount.

A disadvantage of the concept is that the telescope only a small part of the sky can be seen, which is located directly above the telescope, respectively. The corrected field of view has an opening angle of only 24 arc minutes. Due to the Earth's rotation, this area will be expanded; also will be moved to the electronic image sensor ( CCD) image in sync with the Earth's rotation, making longer exposures are possible.

However, there are concepts have been developed to expand by moving and possibly deformable secondary and tertiary levels, the potential field in a range up to ± 23 °. It also established a simultaneous observation of multiple regions of the sky would be possible.

Correction optics and detector are mounted directly above the mirror in the primary focus. The unit has with its focal length of only ten meters a very large aperture ratio of 1:1.5.