Guiding Issues

richardlpaul

Here's my setup:

iOptron CEM25 mount, Stellarvue SV102T scope with a Stellarvue 50mm guide scope.

The ASI120MM mini is plugged into the Guidescope and is in focus. The ASIAIR can see and control the camera no problem.

ASIAIR is plugged into the CEM25 mount with the USB-Serial cable (not using the ST4 port).

The mount is level and has been polar aligned, and the scope aligned with a 3 star alignment. GOTO is working with objects appearing in the field of view.

I have had two problems on successive evenings:

Error message "Alert: Calibration computer RA/Dec axis angles that are questionable"

Error message "Alert: Your Max RA Duration setting is preventing PHD from making adequate corrections to keep the guide star locked. Increaset the Max RA Duration."

I also got this last message in term of the Max Dec Duration.

I have increased the Max RA and Dec durations from the default 500ms to 1000ms, 2000ms, and 2500ms. I keep getting error message.

Any help, most appreciated!

chuckwagon

PHD2 guide questions are probably better asked at the PHD forums, since it is highly unlikely to be the camera at fault. However, I would suspect that your guide rate may be a little low for the camera/scope combo you list. Optcorp lists the focal length of the Stellarvue 50mm guide scope as 210mm. If that is the case, then the the pixel scale of that scope with the ASI120MM Mini is about 3.68 arc-sec per pixel. At the default guide rate of .5x (50% of sidereal) which is the norm for the CEM25 mount, it will take fairly long guide pulses to detect any motion. So I would start by setting everything to their default settings, and then change the guide rate to 1x and see if that helps. Use the guiding assistant and see what it recommends when you have the rate at 1x. If the error messages go away, but your guiding at 1x is unsatisfactory, and you would like to guide at a lower rate, start backing off the rate at .1 increments, for example use .9 then .8, etc. until you get better guiding, or the errors come back.

Good luck

Charles

P.S. - Have you verified that guide pulses actually move the mount? Everything may seem connected properly, but if the guide pulses aren't getting through for some reason PHD2 see that as taking too much time. Try using just the mount and camera with PHD2 using a serial connection, no ASIAIR, and verify that you can indeed guide the mount. That will remove one variable from the mix.

richardlpaul

Thanks Chuck! Will try all your suggestions once the weather clears here. Believe it or not, Tucson has gotten snow the last two days in a row!

Sam@ZWO

this is just one warning and you can ignore it