I am using an SBIG-8300M camera with PHD2 using the SGP Api Guider. I observe that when using a 0.5 second exposure time in PHD2, I can hear the shutter on the built-in guide camera cycle at a rate faster than once a second. But examining the PHD2 Guide log and the Debug log, these show that the cycle time for image, download, analyze and ouput corrections is happening at a cycle a little over 2 seconds, with most of the time between issuing the command to take the image and getting the response.
Why am I hearing the shutter cycling much faster than the commands from PHD? Might SGP be commanding repetitive exposures at 0.5 seconds rather than waiting for a command?