Problem with autoguiding MaximDL

[konstantinos75]

Hi
During a multiple nights CCD astrophotography I faced a problem with autoguiding. I used MaximDL to make the autoguiding over the ST4 port of my mount.
The first night all went successfully. I took 20x10min exposures in Ha. Dithering was set to be 3 pixels between the exposures. Then I parked the scope and did not dismantle it.
The second night, I configured MaximDL to capture 60x1min exposures in every filter R,G,B for the same target as first night. Dithering was set to be 2 pixels between the exposures. Autoguiding went wrong. My frames ended up with elongated stars. Then I parked the scope and did not dismantle it.
The third night, I configured MaximDL to capture 30x1min exposures in R filter for the same target as previous night. Dithering was set to be 2 pixels between the exposures. Autoguiding went again wrong. I received an error message from MaximDL that autoguiding went wrong.
I attach the tracking graphs for three nights plus the MaximDL track logs for nights 2,3.
Does anybody has an idea what went wrong with autoguiding the second and third night?
Thank you
Konstantinos
www.albireo.gr

P.S. the target was IC 1871 in Cassiopeia

[konstantinos75]

I did some research on this issue by studying better the MaximDL tracking graph.
I strongly believe that my problem was caused by the fluctuation in brightness of the guiding star in nights 2,3.
Maybe this was triggered by bad seeing, or some cloud in the upper layers of the atmosphere.
Have a look at the next attachments which prove my assumption of guide star issue.

[konstantinos75]

Maybe this is helpful for some people who don't have a lot of experience with autoguiding in MaximDL.

According to MaximDL manual for best results, place a bright star in the field of view of the autoguider imager, near the center of the field. Take an exposure using the Guide tab’s Expose mode; the guide star will be picked automatically, or you can click on one using the mouse.

My mistake was that I did not select a star near the center of the field. I let MaximDL do this automatically. It selected a star near the edges of the field I don't know why :)

The second night I notice that the guide star was elongated in shape so maybe this was the reason of the brightness fluctuation. I tried to refocus but star still elongated. Maybe bad seeing...

The third night very near the selected guide star there was another star. Maybe the other star affected the guiding.

Next time I will follow manual advice.

[dcalleja]

I actually leave my guide stars slightly off focus. I find if they are really well focussed maxim can loose the plot. My guider is an OAG STi