Building & Using a Tracking Mount for Astrophotography

Aligning the Green Laser With the Hinge Pin

The green laser is installed in an adjustable mount, much like a telescope's finder scope. The method to align the laser beam to be parallel to the hinge pin is as follows:

  • Lift the upper mount plate, disengaging the two gears.
  • If necessary, spin the large gear so that it is snug against the upper plate.
  • Turn on the laser, noting the spot where the beam hits a distant target.
  • Rotate the plate through about 90 degrees.
  • If the laser beam is not parallel to the pin, the laser spot will move on the target.
  • Adjust the laser in its mount (via the 6 nylon adjustment screws) until the laser spot no longer moves on the target when the plate is rotated. When that is achieved, the laser beam is parallel to the pin.

When the camera is pointed north of the celestial equator as shown below, the laser and its mount can be  removed to avoid interference with the camera and its monitor.

 This image shows the green laser and its mount removed from the top plate to give clearance for the camera.

The views and opinions expressed in this article are those of the author and do not necessarily reflect the views and opinions held by dpreview.com or any affiliated companies.

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Comments

Total comments: 4
NancyP
By NancyP (Jan 17, 2013)

What is the maximal load the home-made barn-door mount can accommodate?

What is the minimal wattage on the green laser? I understand that these green lasers often emit eye-cooking infrared, and would like to use the least powerful laser that can be used for polar alignment. I know some people use more powerful lasers for group lectures during star parties, but that capability I don't want.

0 upvotes
RustierOne
By RustierOne (Mar 25, 2013)

Hi Nancy,
I don't know the minimum wattage, since that would depend on circumstances. The visibility of the laser beam depends not only on its wattage, but also on the amount of particulate matter in the air available to reflect the laser beam. I purchased my Laser from Orion Telescopes for around $40 US PPD. It's rated at <5mW, which seems to be very bright in a dark sky. One important use consideration is to be very sure not to point the laser beam at anyone's eyes or at any aircraft. To do otherwise would risk eye injury and would be violation of the law.

Best Regards,
Russ

Comment edited 2 minutes after posting
1 upvote
Leif Goodwin
By Leif Goodwin (Dec 25, 2012)

This mount was invented by George Haig of Glasgow, and originally known as the Scotch or Haig mount. In North America it became known as the barn door mount. The original version had a straight drive arm which accumulated tracking error, which was corrected in later versions with various modifications. The original article appeared in Sky and Telescope, April 1975 according to Wikipedia, where there is a discussion of some of the variants.

0 upvotes
the jimmy
By the jimmy (Dec 20, 2012)

Good article, thanks

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Total comments: 4