The other night I finally got a chance to try a new tool out at the “dark” skies at the Spartan Observatory. Though just north of Geneva city limits, the site’s strength is the near-complete lack of glaring street lights nearby. It’s still close enough to the city, however, that I would anticipate at Bortle scale rating of around 5-6.
The new tool is called Astrotracer, and it’s a function of the Pentax GPS unit when used on some of their DSLRs. Mine happens to be a K5sII. It’s rather clever. First, the GPS does a highly accurate alignment (you have to roll the camera like an airplane: roll, pitch, yaw. Then you put it on a tripod and start an exposure, up to five minutes. Astrotracer then uses the camera’s sensor gimbals, usually used to counteract the effects of shaking to keep images from blurring, to “track” the night sky.
As the earth spins in its daily orbit, the stars (just like the sun and moon) appear to rise, cross the sky and set. Astrotracer compensates for this apparent motion in-camera. It’s like having something between a barn-door tracker and an equatorial mount, inside the camera.
The results were impressive. I was using a 30mm lens, yielding a “normal” field of view on my APS-C-sized camera. The Orion image above was exposed for two minutes; the Gemini one below for three. The Orion Nebula is visible in the middle of the belt. The trees, which are blurred from movement of the sensor, probably aren’t in the best spot in this portrait of Gemini, the twins. Castor and Pollux are visible just above the treetops. In the upper left, you can plainly see the Hyades in the upper left. The stars in the center of both images appear to be tracked better than at the edges. The tracking isn’t perfect…I’ll have to search the interwebs for any tips other Astrotracer users might have.
This is very easy astrophotography and doesn’t take much gear or set-up time, which is nice since I have an abundance of neither (the trailer is short on storage space and life is just short in general!).
More to come!