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.

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.

My homemade sky tracking gizmo.

This is the Andromeda Galaxy. At 2.5 million light-years away from the earth, Andromeda is one of the closest galaxies to the Earth. Andromeda is actually fairly large in the night sky, but it is very dim. I took about 840 images with a Nikon 300mm, f2.8 manual focus lens for a combined exposure time of about 7 hours. There are actually three separate galaxies in this image. The small light smudge below Andromeda is a small galaxy called M110. M110 is 2.9 million light-years away from earth. The fuzzy looking “star” on the upper edge of Andromeda is another small galaxy called M32. M32 is 2.65 million light-years away from earth. All the smaller stars in the image are stars in the Milky Way between Earth and Andromeda. These stars are much closer to us and are probably only 50-70 thousand light-years away from Earth.

This is the Orion Nebula. It is about 1,340 light years away from earth. You can faintly see the Orion Nebula as the center “star” in Orion’s “sword”. This image is about a 7 hour exposure made by stacking 30 second sub-exposures taken with a Nikon 600mm, f4 manual focus lens.

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.