AstroTrac Long Exposure Widefield Images

The following are a series of widefield images taken in October, 2008, from 30 miles north of San Antonio, Texas, with a Canon 400D (Hap Griffin-modified) with a Nikon 35 mm f/2.8 lens mounted on an AstroTrac tracking platform. The full size images are resized to 2000 pixel images to make downloads managable.
The lens is an older Nikon, from the mid-1960s, so it's edge performance isn't great. The lens was stopped to f/5.6 to control coma and limit skyglow from San Antonio lights. One of the goals was to get constellation images where the main stars remain recognizable and are not swamped with smaller stars, so stopping the lens down also helped with this.
Subframe exposure was six minutes at ISO400. Image stack size was either 5 or 6 subframes, depending on how many clouds crossed the images. The AstroTrac was polar aligned once using the unit's own polar scope. One of the great things about the AstroTrac is since an autoguider is not used, passing clouds do not loose tracking lock. As long as there is tracking time left on the tangent arm screw (almost two hours of tracking is available before reset is required), more exposures can be taken to compensate for passing clouds without worrying about the loss of a guide star.


Cassoipeia

Cassiopeia, Canon 400D, 5x6 min, ISO 400, 35mm, F/5.6

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Cygnus

Cygnus, Canon 400D, 6x6 min, ISO 400, 35mm, F/5.6

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Gemini

Gemini, Canon 400D, 6x6 min, ISO 400, 35mm, F/5.6

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Orion

Orion, Canon 400D, 6x6 min, ISO 400, 35mm, F/5.6

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Taurus

Taurus, Canon 400D, 6x6 min, ISO 400, 35mm, F/5.6

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