PhD Guiding Issue

[mick pinner]

when setting up my Orion guider l get a message that says RA calibration failed because star did not move enough. any reasons or ideas on this issue?

[peter_4059 (Peter)]

There's a setting in the brain menu - think it is called calibration step size. If the star doesn't move enough you can increase the step size and it should fix the problem.

[pvelez (Pete)]

also, be careful that you are not guiding on a hot pixel - they never move! Try a few different guide stars as you might find that the dot you think is a star is in fact a hot pixel or some other form of artifact

Pete

[TrevorW]

I've not yet had to touch PHD's step size etc just find another star to guide on this usually fixes the problem

Cheers

[celstark (Craig)]

95% of the time when I get this question from someone it's because the guide commands aren't actually getting through. Connect to the mount and fire up the Manual Guide dialog. Each time you press a button, it will send a pulse to the mount (length = calibration step size). I listen to my mount to try to hear if the commands are changing the sound of the motors. Others can look at the motors or get creative (the mount won't visibly move of course). But, verify that the signals are actually getting through. If they are (the star should have at least moved a decent chunk), then try upping the calibration step size. If this is the problem, odds are you're on a pretty wide guide rig and/or use a mount with a very mild guide correction speed.

Craig

[mick pinner]

thanks guys, l was guiding near the pole and assume this was part of the problem. l upped the calibration steps to 1200 m/s and this fixed the issue.
Craig, l am using a 100m f/9 guide scope guiding a 200mm f/5 imaging scope on a G11, would changing the guide rate on the mount have an effect guiding accuracy?

[celstark (Craig)]

Mick,

Changing the guide rate probably won't help you unless you're guiding very slowly right now (and are too slow to keep up with the errors in your worm). For your rig, bump up the calibration step size though to 2s or so to let it calibrate faster and drop the min motion way down to something like 0.1 or 0.05 as it won't take much motion on that 100mm guide scope to translate into real error.

Craig

[g__day (Matthew)]

It can be helpful to download the calibration check file - view a star the issue (one at a time the slew + RA, + DEC, - RA then -DEC, then clear all to ensure your star is moving. If it doesn't - you likely have a port or wiring problem. If the star does move correctly - then step size being too smal is the usual culprit for calibration not taking.