Originally posted by biz-engineer From the GPS, the position of the camera is known, but the orientation of the camera relative to polar star can only be known from getting correct compass information, otherwise the software couldn't know in what X,Y direction the sensor should move to track stars. An error from compass translate in sensor motion that does not completely compensate for the relative motion of stars, and the error gets more visible when the focal length gets longer.
Thanks, that's very helpful, I had no idea there was a compass within the camera. I'll remember to calibrate with the tripod attached next time I try for the Milky Way. Afraid that won't happen until next summer