What is wrong with this tracking?

[jnb]

I've been trying to see what I can manage with my current unguided setup. I have a set of frames (8 x 120s, 20 x 60s) and notice the tracking is not very good. Part of that is simply down to inadequate polar alignment, part I do not understand. Zooming in to a conveniently recognisable patch of the image I get the following

The gradual drift of the image south is clearly inadequate PA. Why does the rest of the drift seem to vary it's pattern? I would have expected either random directions on all frames from poor seeing causing a smearing of every frame. Or a consistent deviation on all frames from mechanical or alignment issues. What I instead see is that a lot of the frames show a consistent drift during the exposure but the orientation of that drift varies. So for example at 23:14,23:16 the drift is NE-SW, but at 23:21,23:23 it is E-E, at 23:35, 23:38 it is NW-SE. There are a few frames (23:25, 23:27, 23:37) where it seems to change direction mid exposure but not as many as I would expect.

So what's causing the drift and without guiding what can I do to eliminate it?

The mount is a Bresser Exos2 with motors but no goto (I have a goto unit for it but haven't got around to fitting it yet) that's basically Bresser's version of the EQ5.

[D4N]

Some of those look what I see if someone walks past the mount or there is a gust of wind.

Sent from my iPad using Tapatalk

[xtreemchaos]

 i had something the same a wile back,ive got the eq5 with tracking motors it turn out to be the worm screw needed adjusting there was too much play.

[kalasinman]

There seems to be error every 10 minutes. Could be PE of your mount.

[kens]

My money is on periodic error as well

[silios]

My money is on periodic error as well

more money on PE.

I use to get that before guiding.

Tried to record the PE and load it to eqmod but things didn't get significantly better.

Sawed the finder scope, plugged in and QHY5 and never looked back!

[graemlourens]

Just something that happened to me: I had similar effects, but i had my scope on a grassy ground, and the mount was gradually (not visibly noticeable) sinking in one leg at a time causing irregular trailing.

[jnb]

OK, Lining up on a convenient hot pixel and manually stacking all images I have this ...

Which looks like a periodic error every 10 minutes. Which would be consistent with a 144 tooth gear on the RA axis. Obviously the bigger error is from polar alignment, or perhaps more accurately misalignment, but even allowing for that there is still a noticeable periodic error. So, without guiding, what can I do to eliminate that? 

[Leveye]

My mount has PEC in the handset to correct for that. I still think some of this was wind.

[jnb]

Wind is quite possibly the source of some of that (e.g. the big EW movement at 23:24) but there is a progressive element which is polar alignment (gradual north south drift over the 40 minutes) and a periodic element which now appears to be a mechanical periodical error (a tendency to swing East at 23:20, 23:30, 23:40, 23:50). Both of those I may be able to do something about albeit that I do not have guiding or PEC in the hand control. There is very little I can do about wind.

[kens]

Nice detective work. I've spent much time myself making worm images.

Have you worked out the extent of the PE? My rough analysis puts it at around 34 arc-sec peak-peak.

You might reduce it a little by fine tuning the mount but I think somewhere along the way you'll  need to bite the bullet and start autoguiding.

My moment came when I was able to reduce the N-S drift to just a few seconds so the PE stuck out like the proverbials.

For wind, just lay off the baked beans.