Astrophotography Sky Tracker (2009)

I wouldn’t say that I’m really into astronomy, but I do like the idea of the infinite vastness of space. I have wanted to try astrophotography for some time, but my main problem with astrophotography was that the cost of a telescope capable of doing what I wanted was outside my budget for a short term photography project.

 

Michael Fuchs Sky Tracker
Michael Fuchs Sky Tracker

My solution was to design and building a very simple all-mechanical camera mount that would passively rotate at the same angular speed that the earth rotates.  I knew I couldn’t make anything that could track accurately for hours, but I thought that I could probably make this tracking mount accurate enough to take 30-60 second exposures without noticeable motion blur.  The tracker runs on a set of nice ball bearings and is completely mechanical.  It uses a simple homemade gearbox, a curved threaded lead screw, and a normal clock motor to move the camera at the same rate that the earth rotates.  When the tracker rotational axis is properly aligned with the North Star, the tracking error is unnoticeable for exposures up to about 60 seconds.

I solved the long exposure image noise problem by simply avoiding the problem altogether.   I take 30-60 second exposures one-after-another for 7-8 hours.  This effectively gives me ~6 hours of gathered light information in something like 800+ separate image files.  I can take all the “sub-exposures” and “stack” them to get a final image with an equivalent exposure time of many hours.  By dividing up the exposure this way, it is fairly easy to line up all the stars in the image from one frame to the next, effectively eliminating any tracker error.  This technique also subsequently improves the image signal to image noise ratio of the final image.  This “image stacking” method is by no means new or original.  This is the same basic technique that NASA uses for processing Hubble images.

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