How do we determine what pixel to put here? Im currently imaging at 1.59 arc/pix.
thanks
The value is in units of guide camera pixels (not imaging camera pixels). It is useful to think in terms of arc-seconds, and use the guider pixel scale to convert arc-seconds to guider pixels.
If your guiding is dialed in you should be able to reach guiding total RMS error = seeing / 4. If your seeing is poor (4"), that would be 1 arc-sec total RMS error. For 1" RMS you could probably tolerate short spikes of 2-3". Assuming your guider pixel scale is 2"/pixel that would be 1.0-1.5 guider pixels. So a 1.5 pixel limit might be appropriate, or you could be a bit conservative and go with 2 pixels.
Ultimately the value you choose will depend on your gear and conditions (wind, seeing), and what error you are willing to tolerate.
Caveat: PHD will never report a guide error greater than 2.55 pixels to SGP, so if you set the value in SGP to anything over 2.55 it will never trigger. This is a limitation of the PHD1 server interface. PHD2 has a new server interface and the forthcoming SGP 2.4 uses the new PHD2 server interface and this problem no longer exists in SGP 2.4.
Andy
Thank you.