SGP with PHD2 and SGPApi guider

Greetings Group,

I have an odd problem in that my cameras do connect and everything seems to function as expected but I suspect that my PHD2 statistics are flawed. I image with a SBIG STT8300M CCD with the FW8G which has a remote guide head. As you know, to use these two cameras on the single USB connection requires the SGPApi Guider to be selected as the camera. This works fine. However, once PHD2 is guiding and reporting my guiding statistics I noticed the accuracy to be much better than in the past. Upon further inspection I noticed that the guiding camera pixel size is being reported as 1.0 micron where it is actually 7.4 microns. This would account for the good stats as a one pixel deflection would account for only one seventh of the actual movement.

The folks at PHD2 report that this number (pixel size) is called from ASCOM. I could find no ASCOM log for this date but I have provided a link to the other pertinent logs.

I did find that the PHD2_DebugLog contained both correct and incorrect “pixel size” entries but I cannot determine why.

Any insight you can provide would be helpful.

PHD2 2.6.6 Dev 1
Windows 10



I’m not sure what you mean here… SBIG does not use ASCOM drivers. I can’t remember for certain, but can’t you manually set the pixel size in the PHD2 profile?

Both the imaging camera and the guiding camera use a single USB cable and essentialy connect to two different software programs (SGP & PHD2 in my case). The SGPApi Guider acts as a traffic cop to direct image frames one direction and guiding frames another. The cameras are using SBIG drivers but the camera selection must be “SGPApiGuider”. This is only the case for SBIG cameras with the “built in” guide camera. When selecting the SGPApiGuider, the pixel size option is greyed out.

In viewing the PHD2 DebugLog I can find the call for pixel size returned in both the correct 7.4 micron and incorrect 1.0 micron amounts.