Last weekend was my first attempt to use the internal autoguider since I usually use PHD2. I saw that I could export the guiding data so being the geek that i am, i downloaded the from the 100 minutes of capturing M27. During the imaging session I was capturing 1 minute subs. When i opened the data and charted it in Excel I noticed there was a significant spike in the RA error every 10 minutes of the capture session. Any idea what I should be doing to correct or at least minimize this? I am using an older Meade LXD55 mount if that helps.
You can understand much more of what is in the guide log if you open it in PHD Log Viewer. adgsoftware.com/phd2utils/
Those could simply be dither pulses, and this application will show that. It will also filter them out and show you a detailed frequency analysis of your periodic error.
Every 10 minutes? I *think* that may be periodic error.
"Even quality machined mount parts like worms, worm gears, shafts are not absolutely perfect. The parts are machined in micrometer precision at best. We must realise that in astrophotography we require tracking precison up to arcseconds. That means, that e.g. teeth of teeth on perimeter of wheel with diameter of 8cm must be machined with accuracy of hundreeds of nanometers!
As mount's shaft rotates, any error in its surface and shape and also in worm and worm gear surfaces and shapes causes a periodic bump in tracking. The most observable is so called periodic error of the mount which is caused by inaccuracy of of worm. The period of this error takes one revolution of gear (usually 5-10 minutes for common mounts)." ~http://www.pk3.org/Astro/index.htm?astrophoto_mount_errors.htm
Unfortunately I won't be home until Saturday to review what my settings were for this run. I'll post it then.
As far as the periodic error, I wondered about that at first but I thought that would be demonstrated by a gradual drift in one direction followed by a drift in the opposite direction as the worm wheel rotates. That doesn't appear to be the case here.
You are correct, looking at the raw guide data would not create a such a regular peak due to periodic error, unless maybe there is some physical grit in the gears or something.
I'm inclined to say they are dither pulses, but that only makes sense of your images are 10 minutes long, or if dither ever N frame, a factor of 10.
Upload the original guide log, that will make it much easier to see what is happening.
I experience something similar when using the ASI120MM (USB2 version).
That camera does not work well with Linux. Without the firmware update it did not connect at all and with the firmware update it keeps dropping frames intermittently.
What I noticed is that it drops frames or only receives part of a garbled frame every time a new image is being downloaded from the main camera. That results in the guide star being lost/displaced and the guider frantically starts looking for it, resulting in a huge deflection. Unless the guide star is reacquired right away, the next exposure is ruined by star trails.
Bottomline: The ASI120MM is useless under Linux and should not be used or sold to Windows users.