scopesnc The calibration is set at 4100. If I go over that it tells me every time It could not do enough steps and may not work right.
If you had set your mount's guide rate at 0.5x sidereal rate, the mount will move about 7.5 arc-seconds per second of time that you had set as the duration of "Calibration Steps" (which is in miliiseconds). In your case, every calibration step (4100 milliseconds) will therefore correspond to about 31 arc-seconds of movement.
To determine what PHD2 needs, you will need to convert the angle in arc-seconds into the number of pixels on your guide camera.
For this (the so called "plate scale"), you need to know two things: 1) the size of a pixel, and 2) the focal length of the guide scope. if you recall, for small angles, the sine of 𝜃 is simply 𝜃, so the displacement on the sensor in mm is focal length in mm * 31 arc-seconds (in radians). Dividing by the pixel size then gives you the number of pixels per "calibration step."
There are tools on the web to help you do that in case you don't want to calculate it yourself. This site (courtesy of FLO that UK hobbyists may recognise) for example, shows that a 250mm focal length OTA when combined with an ASI290 camera, has a plate scale of 2.39 arc-seconds per pixel.
https://astronomy.tools/calculators/field_of_view/
Once you have that, you will know how much each "calibration step" will move a guide star by.
To perform the guide calibration, PHD2 wants to move the calibration star by 25 pixels (not arc seconds). If the step size is too small, PHD2 will give up, and you end up with the diagnostic message that you saw. Aim for roughly a dozen "calibration steps" to move that 25 pixels.
If you have a nice pier-mounted premium mount, and a night with clear seeing, a couple of steps is sufficient. For your mount on a tripod, I might suggest a bit more than 12 steps to average out any mechanical error.
If you don't want to do any calculation, just blindly increase your "Calibration step" duration so that PHD2 moves by 25 pixels in, say 15 steps. If it needs to move more than 15 steps, increase the "Calibration step" duration. If it completes the 25 pixels in fewer than 8 steps, decrease the "calibration Steps" duration.
Just remember that "Calibration Steps" in ASIAIR is not a distance, but a duration in milliseconds. It really should be called "Calibration Step Duration."
It is incredibly stupid for ASIAIR (since it claims to be simple to use) not to automatically set that duration to keep PHD2 happy, since it already knows what it takes to keep PHD2 happy, and it knows the focal length of your guide scope, and the pixel size of the guide camera. The GUI should just let you set the number of steps for PHD2 (and limit that number to be say in between 8 and 20), and defaulting to 12 for the novice user. At least, that would be the GUI that I would design.
Chen
