Hi Gary, thanks for the three explanations. I tried to see if the encoder reading changed - it clearly did NOT. Hence, we are looking at slight sagging or camera shift. I actually got around this problem by using the great spiral search feature. Important to do this at the low speed, high magnification setting. The latter requires the speed switch on the front panel to be changed. In this way I can easily reacquire the star if it slips outside the field. -Mikael