Hi all...I sometimes wonder if I will ever take an image!!!

Here is my imaging scenario.

Guiding through 12.5" RCOS with ST10XME (using main chip as guider), guider binned 3x3, guider image scale 1.46 asp
Imaging through FSQ with STL11K, image scale 3.5 asp.

Calibration results
X -3.727
Y = 14.39

Maxim Settings

Min Move X - 0.12
Min Move Y - 0.10
Max Move X/Y - 1.4
Agg X - 3
Agg Y - 9

The Min Move settings above were originally taken from Autoguider Calc v4.02, but were lessened. The actual Min Move value from the calculator is 0.17. Below is an extract from the Maxim guide log.

Off X Off Y Corr X Corr Y
12:43:04, 394.57, 275.43, -0.43, -0.57, 0.00, 0.00, 17418
12:43:13, 394.64, 275.40, -0.36, -0.60, 0.00, 0.00, 20482
12:43:21, 394.32, 275.83, -0.68, -0.17, 0.00, 0.00, 21532
12:43:29, 394.21, 275.22, -0.79, -0.78, -0.13, 0.00, 18448
12:43:36, 394.16, 275.36, -0.84, -0.64, -0.13, 0.00, 18171
12:43:44, 394.69, 274.77, -0.31, -1.23, 0.00, 0.00, 21832
12:43:52, 395.02, 275.75, 0.02, -0.25, 0.00, 0.00, 21970
12:43:59, 395.13, 275.21, 0.13, -0.79, 0.00, 0.00, 22928

Throughout this entire 15 minute image, no corrections were sent to Y at all (Yes, corrections are enabled, and calibration routine was normal suggesting the cable is fine....this PC has no connection to the telescope).

Here, we see two consecutive corrections sent to X when the offset was -0.79 AND -0.84, but as you can see, there are at least 3 occasions in this small portion alone when the Offset in Y is just as great, or even larger. There were many occasions when the Y pixel error was over 1 pixel. Now, with the Min Move for Y set to a smaller value than X...Why are no corrections being sent to the mount? Consequently, my guiding (or rather lack of it) is all over the place and my images are crap.

Sure I can drop the Min Move value down to 0.01, and I see corrections being sent, but if I try to follow the rationale of guiding, I will be sending corrections all over the place for no reason.

grateful if someone could offer a possible explanation as to why this is.

tks

Martin

Hi Martin,

Does the calibration for Y appear normal to you?

For all the mounts I've used, calibration in X and Y are usually very similar. Could this be the issue? Which mount do you use? And do the X and Y calibrations normally appear this different?

The things that normally account for such a large difference could be either large DEC backlash, or large backlash compensation setting on the mount and/or in software.

Regards,

-Paul

Thank you Paul

No, the Dec calibration does not seem correct at all, and indeed, typically the X/Y values are close. However, sometimes you have to reduce the Y calibration time compared to the X calibration time because the mount (ME in my case), would be far more responsive in that axis then it is in X....so different calibration times would yield different results, but not to the extent shown here.

I must admit, my mount is way out of balance because of the addition of an FSQ to the RCOS.
That is now fixed with the acquisition of a new weight just yesterday.

I will retest.
cheers

martin