An Inexpensive Tracking Mount for Astrophotography

Started Aug 24, 2012 | Discussions thread
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An Inexpensive Tracking Mount for Astrophotography
Aug 24, 2012

I would like to share my experience in making an inexpensive tracking mount for astrophotos. My original post has been to the Sony NEX forum, so I apologize if this is viewed as “forum hopping” – no offense intended. But the mount is universally adaptable to any modern digital camera. So I would like to share my experience with this forum to encourage others to construct the Barn-door Mount . While it is capable of tracking for an hour or more, good results can be obtained with just a two-minute exposure. In the following link you can view a number of Milky Way images and mosaics obtained with this type of mount.

Below is the Barn-door Mount with camera on a Celestron equatorial wedge, which aids in polar aligning the mount.

This is the whole mount, wedge and Celestron tripod. The wedge and tripod are from a 1976 Celestron-5 telescope.

The key to this type of mount is the piano hinge between the two plywood halves of the mount. The upper plate moves relative to the lower one via that hinge. The hinge pin must be pointed at the North Celestial Pole (near the North Star) for the northern hemisphere.

The 10-32 threaded brass rod, which drives the mount, is curved to a 7.1-inch radius. It is driven upward by a nut epoxied to the bottom of a gear turned at 1 RPM.

The 4 RPM DC gear-motor drives the upper plate via set of spur gears (16-tooth and 64-tooth, giving a 1:4 ratio). Motor speed is adjusted with a small variable DC supply (visible in the image below) powered by a 9-volt battery.

If the mount is set upon a photo tripod, the photographer can just sight along the hinge pin to align it with the celestial pole. Since the equatorial wedge gets in the way on my setup (preventing sighting along the pin) I installed a green laser to be parallel to the pin. This laser beam is then pointed at the celestial pole via adjustments on the equatorial wedge ensuring that the hinge pin is polar-aligned. This image (below) shows the camera pointed south of the celestial equator.

When the camera is pointed north of the celestial equator (as seen below), the green laser and its mount are removed to avoid interference with the camera.

The green laser is installed in an adjustable mount, much like a telescope's finder scope. The method to align the laser to be parallel to the hinge pin is as follows. Turn on the laser, noting where it hits a distant target. Lift the upper mount plate and rotate it through about 90 degrees. If the laser is not parallel to the pin, the laser beam will move on the target. Adjust the laser mount until the laser spot no longer moves on the target. When that is achieved, the laser is parallel to the pin. The center nylon screw in the image below activates the laser push-button switch.

The term “inexpensive” for this mount is of course relative. I estimate that my mount has cost around US$185. Major parts utilized in the mount are from the parts list in an article on pg. 80 in the June, 2007 issue of Sky and Telescope magazine “Build a Tracking Platform for Your Camera” (by Gary Seronik). Added to the above cost would be a heavy-duty photographic tripod which can easily cost over $100.

Take note of the following link to “Mounts for Astrophotography” by Jerry Lodriguss

In that reference Jerry states “… good, inexpensive German-equatorial starter mounts for astrophotography are difficult to find for less than about $750 - $1,000.” So in light of that fact, the roughly $200 cost of the Barn-door mount is quite reasonable.

A commercial source for a Barn-door type mount is for $580 plus shipping.

Several forum members have used the Celestron CG-5 equatorial mount ($690 + shipping from B&H photo) to take some very fine Milky Way images. Here's wishing you success with your astrophotography. Modern digital cameras are quite capable for such an endeavor.

Best Regards,

 RustierOne's gear list:RustierOne's gear list
Sony Alpha NEX-5N Sony Alpha NEX-7 Sony E 18-55mm F3.5-5.6 OSS Sigma 19mm F2.8 EX DN Samyang 8mm F2.8 UMC Fisheye +3 more
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