Re: Consequence of .5 guide on hand controller and 1x in software?

Roland Christen

.5x slows everything down, so it takes twice as long for the mount to respond to a move command. the way mounts work with autoguiders is the following: The guider takes an exposure and determines that the mount is off by a couple of pixels. It sends a command for the mount to move that amount, and ideally it would like to see it move instantly to the proper position. At 1x sidereal it takes 1 second to move 15 arc seconds. It takes 2 seconds at .5x and 4 seconds at .25x. That would seem to be fast enough, and for RA it might be unless you wanted to recover quickly from a 10 arc sec dither. However, there is also the Dec axis to consider. In almost all mounts, even ones with spring loaded worms and belt drives, the reversing backlash delay is anywhere between 10 and 20 arc seconds, so for really tight guiding in Dec you want the mount to be able to respond in a timely manner to a Dec reversal command. It might take a second at 1x sidereal, but at .25x it may never get there before the next move command is issued. That compounds the problem and the axis could very well overshoot if the aggressiveness is set too high.

The reason the lower guide rates were ever considered goes back to the days of hand guiding where the user would try to keep a star on a crosshair. At 1x sidereal the mount moves rather quickly at 15 arc sec/sec. Many people do not have fast response, in fact some have eye - hand response rates of up to 2 seconds. So, the .25x rates were set to make guiding a bit less frantic for the manual guide user. Autoguiders have no such limitations. The CPs can be set up to guide at 12x sidereal and still work perfectly fine. In fact, that's how the mounts with absolute encoders do their magic, the guide rate is a variable depending on how far the mount must move during Dec reversal.


-----Original Message-----
From: Tom Blahovici <tom.va2fsq@...>
Sent: Sat, Jun 5, 2021 12:48 pm
Subject: [ap-gto] Consequence of .5 guide on hand controller and 1x in software?

I have been guiding pretty well although at times, it seems to be erratic. I always though that this was seeing.
A recent thread mentioned guiding rates should be 1x in software and the hand controller. So I checked to be sure. Sure enough, the hand controller was set to 0.5x instead of 1x.
How will this effect guiding? I've had it like this for years, but have never been perfectly happy with the see saw RA graphs and the 100% agreesiveness needed for the Dec axis.
Any comments? Could this be a cause?

Roland Christen

Join to automatically receive all group messages.