O-GPS1 vs Built-in GPS Guide

Findings

We found, consistently, that the camera's generation was the most important factor for astrotracking duration with all other factors (lens, light, camera placement, and calibration) being equal. Also, regardless of the GPS system, the camera's angle relative to both the polar direction and the horizon has significant effects on tracking duration. Lastly, calibration efficacy had a significant effect on astrotracking duration, more so even than lens focal length.

We advise that anyone wishing to use either the O-GPS-1 or the on-board GPS for astrotracking practice first. Even if you live in a city and can see only two stars, practice your calibration technique and see how long the exposures of those two stars can be with the lenses you plan to use when you take your actual photo. Practice this nightly, if possible, for a few weeks before you go out to take your actual photo. Perfecting your technique and understanding your camera's limitations before the shoot will set you up to make the most of your actual shoot time.