From: Milton Aupperle <milton@outcastsoft.com>
Date: October 6, 2007 5:29:40 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Re: Purchased a new straight thru RJ-12 cable
Hi Tim;
On 6-Oct-07, at 4:51 PM, centurion40tim wrote:
Rats. May try again tonight if weather eases up. I am using my main 9.25 scope for
guiding while I am learning. Have not made any adjustment to the guide rate. I was mainly
after a simple button test.
With a C9.25 and the camera at prime focus, you should immediately see movement as your getting is 0.5 arc seconds per pixel. At 50% sidereal rate for every 1 second of right or left button time it will move 15 pixels on screen.
On the Celestron yahoo site they are saying that the default autoguide rate is 50% sidereal
which works out to 7.5 arc-seconds per second guide correction - much slower than the
Meade default rate.
The default 50% or 0.5x rate is the same as my HEQ5 too.
I assume that's what it is since I haven't changed it. Most folks are
saying that they bump it to 99%.
It depends on the focal length your using for guiding. At prime focus with a C9.25 using 50% sidereal guide rate, to apply a 0.5 pixel (1 arc second) correction means that we need to turn the motors on for 33.3 milliseconds (0.5 / 15) which is 1/30 th of a second and then off. However there are several inherent lags that cause issues with this, for example times for sending a command over usb which is usually 5 to 10 ms for the GPUSB, some lag times for when timers firing off to stop the motors in OS X (up to 5 ms) and also the lag time in your mounts response to the commands too (unknown and not easy to measure). So if your below about 50 ms for a correction, you can wind up with over or undershoots simply because timing just is not accurate enough.
Will try that. I also found a document on that site so I can
recheck the pinout arrangement vis a vis my new cable.
If the cable checks out, I'd check the pins on the GPUSB too. Basically put the negative probe on the black cable and test each button.
HTH..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta T2R0N5
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