I've been using the AA+ for a few months and have had exceptional guiding. However, during the last couple of session an issue has emerged. I use the Plan method and let AA+ do everything automatically... slew, plate solve, focus and multi-star guide (3 second exposure). During the last two sessions, guiding has been going crazy. When I enlarge the guiding graph, I can see it target a start... then on the next exposure, it jumps to another nearby star... causing a huge correction. Then the next exposure, it will bounce back to the original star and make a huge correction. This continues indefinitely until I manually force it to guide off another star... but then after the meridian flip, it will start messing up again.

Has anyone had this issue? It's unfortunate as the guiding has been impressive... until now.

Thanks,

Ron

  • w7ay replied to this.

    ronaldnc This continues indefinitely until I manually force it to guide off another star... but then after the meridian flip, it will start messing up again.

    Next time, try increasing the guide camera gain by 15 dB to 20 dB (with ZWO's cameras, increase the gain by 150 to 200 units).

    Chen

        w7ay

        Okay. I don't understand what that will do... but willing to try.

        Thanks,

        Ron

        • w7ay replied to this.

            ronaldnc Okay. I don't understand what that will do... but willing to try.

            Please don't do it if you don't understand why, becuase you willl just be randomly tweeaking parameters.

            Chen

              Chen,

              It seems that the guiding is confusing which star to track. There are two stars that are very similar quite close to each other that it switches back and forth in tracking. I'm not quite sure why the multi-star guiding isn't influencing its choice.... that's one of the main advantages. Does it not help?

              Perhaps with making the stars have more contrast (increasing gain) will help it to distinguish the correct star?

              I'll still try it, but this feels like a bug in the guide star detection algorithm.

              Thanks,

              Ron

              • w7ay replied to this.

                ronaldnc It seems that the guiding is confusing which star to track.

                That is exactly why you need to understand what multi-star guiding is doing and not just take my word for it.

                I have over the past few months descibed the process over and over, and tired of repeating myself, so you would just need to search the Forum archives.

                Search (probably a few months ago) a posting that includes the bar chart showing the distritbuion of stars relative to their signal to noise ratio.

                ASIAIR uses signal to noise ratio to weight the centroid averages, and when there are one or two really bright stars in the frame, this SNR weighting causes the equivalent of just one or two stars being used instead of 12 stars, even though you see it select 12 stars (i.e., the weights of the rest of the stars are miniscue).

                When the brightest star scintillates so that the next star is now "brighter," (higher SNR) ASIAIR will suddenly place a huge weight on that other star, while redusong the weight on the previous star, and thus suddenly move the estimated centroid.

                When you increase the gain (by a lot) so that the brightest stars are saturated (and thus ignored), and the remain stars have more evenly distributed SNR, then multi-centroid star averaging will work more like what you expect it to work.

                Until you understand this previous paragraph, I would recommend not just randomly play with the gain. I never believe in telling people what to use. I prefer to tell them what is the underlying factors, and let the folks who are willing to spend time understanding the problem to come up with the solution themselves (... teach a person how to fish and you feed him for the rest of his life...).

                Chen

                  Chen,

                  Thanks!

                  Actually, I understand how PHD2 works pretty well... not so much AA+ guiding. I've used PHD2 for years and understand how to adjust for its "quirks". In PHD2 (which is well documented), you can "tune" it to your instrumentation. I have never had this kind of problem with it. As for AA+... there is not much documentation on how their guiding works, so difficult to "learn" without experimentation. As folks are often told... "it is as easy as A,B,C".

                  What's weird is that the star it kept jumping to did not have the indication that it was even a selected star. That was perplexing to me, as there were several other stars selected.

                  Thanks for your help... sorry you had to explain it all again. Perhaps you can get someone to write it into the documentation.

                  Ron

                  Chen,

                  I continue to struggle with this problem. I've changed gain, used/not used darks, etc. It still occasionally jumps to a nearby star on occasions and issues pulses to move the scope that way. The adjustments are not small! Then it will suddenly move back to the original star and move back.

                  This behavior just started a few weeks ago. Do you know if there was some recent update that changed the guiding logic?

                  Thanks,

                  Ron

                  • w7ay replied to this.

                    ronaldnc Do you know if there was some recent update that changed the guiding logic?

                    I don't know of any ASIAIR update in months.

                    Did you try increasing the guide camera gain as I suggested? When there is scintillation, the ASIAIR will abandon a star that becomes saturated. So, what you want to do is to saturate that particular star to start with, so that it is not even initially picked.

                    Chen

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