Is this Periodic Error?

[RogerTheDodger]

Just want to check before I delve into PEC....

26 1 min frames as an animated gif, I'm pretty sure the slight rotation at the end was the webcam lead catching on the mount.

[anthony]

Does not look like it to me although it will be in there somewhere. At that image scale (I presume that is andromeda) I am not sure you'd see it that much and being periodic it would end back up in the same spot. More likely tied in with polar alignment.

Are you guiding on this?

[RogerTheDodger]

Not yet, I'm in the process of making a finderguider, and yes that is andromeda... I set up the PA with the EQMOD polar alignment, and checked it again 4 hrs later and it was still smack in the centre of the circle. The scope is balanced in both RA and DEC, and I have tried making it heavier at the back when looking east, but I always get this motion.

The odd thing is that these are 60 second exposures, i'd expect to see trails rather than jumps... any suggestions gratefully recieved

[ollypenrice]

I've never seen a video of PE in action but if I had to guess what one would look like I'd say this. It goes up and down in a regular pattern but backlash would also do that. If you are in perfect balance backlash is to be expected. You should aim to be a little heavy on the east in RA, certainly, to let the mount fall onto one side of mesh. (Otherwise it oscillates from one side of mesh to the other.) Maybe run the Dec a little out as well, by experiment.

Olly

[RogerTheDodger]

Thanks Olly, I've been looking for examples and the only one I could find looked more like a starry wiggle, so I think you may be right about backlash. I'll try again with the OTA slightly unbalanced and see if that makes a difference.

[JohnnyD333]

I think Olly is right, when I use my autoguider it states that it is clearing the backlash about halfway through the calibration process. I have never seen a video of backlash in action but that could be the issue.

[RogerTheDodger]

Thanks Johnny.