Guiding and Chasing Seeing
I thought I would explain for those who don't how a mount can end up fighting seeing and you can end up with worse guiding with settings that are too aggressive.
Seeing can temporarily displace a guide star (just like watching the bottom of a pool or pond through ripples on the surface of the water). That displacement is temporary and will change relatively quickly. So say that seeing has displaced the star 1 arc-second from where it is on average. If you have aggressive settings (say 100% aggression), the mount will be told to move to get the star back in the average position. Often times with seeing the star will have already gone back to the center on its own! It is even possible it has moved to the other side of center. Now we have moved the mount unnecessarily.
So it with no guiding, we were 1 arc-second off and the star has now returned to center. But if we were guiding, the star was 1 arc-second off and now is one arc-second off in the other direction. Even worse, consider if the star now moves back to the original position due to seeing. That plus the one arc-second correction in the other direction and we are now two arc-seconds off leading to a huge correction that can cause even further problems.
The bottom line is this. Unless using very fast exposures (video speeds), correcting movement of the guide star due to seeing is detrimental to good guiding.
What you want to correct when guiding are not movements of the guide star due to seeing but movements of the guide star due to tracking errors with the mount/polar alignment.
So how do we distinguish movements of the guide star due to seeing and the mount? If you think about it, like ripples in the pond, if you look over a long enough period of time, the movements due to seeing will have been averaged out leaving just movements due to the mount. So:
1) Using longer guide star exposures can help.
2) Using lower aggression settings can help (since you don't correct the entire movement seen).
Now if you use values that are too long (for the guide star exposure) or too low (for aggression) you won't react fast enough to correct mount problems so the trick is finding the settings that allow you to correct mount movements while ignoring most of the movement due to seeing.
It also really really helps if your mount does not have issues that result in fast movement but only slow gradual ones. Unfortunately, many mounts do not meet that criteria either due to maladjustment, or the inherent qualities of the design.
Seeing can temporarily displace a guide star (just like watching the bottom of a pool or pond through ripples on the surface of the water). That displacement is temporary and will change relatively quickly. So say that seeing has displaced the star 1 arc-second from where it is on average. If you have aggressive settings (say 100% aggression), the mount will be told to move to get the star back in the average position. Often times with seeing the star will have already gone back to the center on its own! It is even possible it has moved to the other side of center. Now we have moved the mount unnecessarily.
So it with no guiding, we were 1 arc-second off and the star has now returned to center. But if we were guiding, the star was 1 arc-second off and now is one arc-second off in the other direction. Even worse, consider if the star now moves back to the original position due to seeing. That plus the one arc-second correction in the other direction and we are now two arc-seconds off leading to a huge correction that can cause even further problems.
The bottom line is this. Unless using very fast exposures (video speeds), correcting movement of the guide star due to seeing is detrimental to good guiding.
What you want to correct when guiding are not movements of the guide star due to seeing but movements of the guide star due to tracking errors with the mount/polar alignment.
So how do we distinguish movements of the guide star due to seeing and the mount? If you think about it, like ripples in the pond, if you look over a long enough period of time, the movements due to seeing will have been averaged out leaving just movements due to the mount. So:
1) Using longer guide star exposures can help.
2) Using lower aggression settings can help (since you don't correct the entire movement seen).
Now if you use values that are too long (for the guide star exposure) or too low (for aggression) you won't react fast enough to correct mount problems so the trick is finding the settings that allow you to correct mount movements while ignoring most of the movement due to seeing.
It also really really helps if your mount does not have issues that result in fast movement but only slow gradual ones. Unfortunately, many mounts do not meet that criteria either due to maladjustment, or the inherent qualities of the design.