Barn door tracker

A Barn Door Tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for observing, or for photography of, astronomical objects. It is a simple alternative to attaching a camera to a telescope which has a motorized equatorial mount. [Gary Seronik, "Build a Tracking Platform for Your Camera" in "Sky & Telescope", June 2007, p. 80.]

History

The barn door tracker was created by George Haig. His plans were first published in "Sky & Telescope" magazine in April 1975. Modified versions of the tracker were published in the magazine's February 1988 and June 2007 editions.

Design

A simple single-arm barn door tracker can be made by attaching two pieces of wood together with a hinge. A camera is mounted on the top board, usually with some sort of ball joint to allow the camera to be pointed in any direction. The hinge is aligned with a celestial pole and the boards are then driven apart (or together) at a constant rate, usually by turning a threaded rod or bolt. This is called a tangent drive. [http://www.astunit.com/tonkinsastro/atm/projects/scotch1.gif] This type of mount is good for approximately 5-10 minutes before tracking errors become evident when using a 50mm lens. That length of time can be increased to about 20 minutes when using an isosceles mount. [http://www.astunit.com/tonkinsastro/atm/projects/scotch2.gif] A curved drive bolt in lieu of either a straight tangent or isosceles mount will greatly extend the useful tracking time.

These designs were improved upon by Dave Trott, whose designs were published in the February 1988 issue of "Sky & Telescope." By using a second arm to drive the camera platform, tracking accuracy was greatly increased, and can lead to exposure times of up to one hour. [http://www.astunit.com/tonkinsastro/atm/projects/scotch3.gif] The most accurate of these designs is the Type-4.

The most basic of these designs are manually operated, although some have added electric motors to automate and improve the accuracy of the tracking process.

References

*Tonkin, Steve. [http://www.astunit.com/tonkinsastro/atm/projects/scotch.htm A Better Barn door]
*Gagnon, Steve. [http://education.jlab.org/tracker/index.html How to build a double-arm barn door tracker]
*De Tray, Jeff. [http://www.astronomyboy.com/barndoor/ Build a Barn Door Tracker]

ee also

*Astrophotography

External links

* [http://www.astunit.com/tonkinsastro/atm/projects/scotch.htm A Better Barn door]
* [http://education.jlab.org/tracker/index.html How to build a double-arm barn door tracker]
* [http://www.astronomyboy.com/barndoor/ Build a Barn Door Tracker]
* [http://thecosmiccanvas.googlepages.com/ The Cosmic Canvas]

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