Posted April 20th, 2012

Orion Nebula

I recently purchased a Pentax O-GPS1 GPS attachment for my camera. While its main purpose of course is to geotag photos, this unit also has a unique astrophotography feature that I just had to try out. Its astrotracer function employs the sensor shift mechanism of the camera’s image stabilization system to move the sensor to compensate for the rotation of the earth during long exposures of the night sky, in effect an equatorial mount for the sensor. After trying it with some wide angle views, I got ambitious, put on my longest lens and aimed it at the Great Nebula in Orion (M42 and M43) along with the Running Man Nebula in the upper area of the image. In order to acquire and define dim details, this image actually consists of 22 40-second light frame exposures of the nebula to accumulate exposure, 16 dark frames for noise reduction and 16 flat frames plus corresponding dark frames to correct for lens artefacts and vignetting, all combined using DeepSkyStacker software. That is a total of 70 exposures ... each image of this type is a small project. The O-GPS1 did not do a perfect job, elongation of the stars is evident. Exposing for 50 seconds, the maximum indicated for this focal length and south-west shooting direction from my location, produced distinct streaking. Shorter exposures down to 20 seconds did not provide significant further improvement from what I used here. You can find better photographs of this subject, though perhaps not taken with such relatively unspecialized, small, light, easy-to-use equipment. But it always excites me when I can photographically extend my vision far beyond that of my naked eye and I feel compelled to share this.
Pentax K-5, Pentax O-GPS1, Sigma 150-500mm f/5-6.3 APO DG OS HSM @ 500mm, 22 x 40 sec @ f/6.3, ISO 1100