O-GPS1 vs Built-in GPS Guide

Astrotracer Reliability

We tested the astrotracer with multiple focal lengths from 10mm to 135mm. As is true of all things with astrophotography, the shorter the focal length, the better the star tracking accuracy will appear (though corners in ultra-wide lenses can be a bit softer). Still, yes, the Pentax tracking systems were fantastic at 10mm and 31mm. Where the difference between the O-GPS1 and K-1 really shows in at the 135mm focal length. We didn't test beyond 135mm because lenses longer than that focal length with suitable speed are rare to non-existent, so telescopes and telescope sidereal trackers become a better solution at that point.

One major factor in astrotracer accuracy was the angle and direction the cameras pointed. We found that the astrotracer performed the best when pointed at Polaris with decreasing accuracy the closer the camera came to being pointed due East or due West. We also found that angling the camera upward reduced accuracy the closer it came to a 45-degree pitch with accuracy at zero and 90 degrees being basically the same. So a 45-degree camera pitch to the East or West will likely deliver the poorest results where as a zero- or 90-degree pitch to either the North, South, or Zenith will likely deliver the best results.