Help needed guiding iOptron CEM60EC

[old_eyes]

OzAndrewJ on Cloudy Nights analused my PHD2 Guidling Logs and diagnosed a bad SDE problem. Intensity was reduced by the beta firmware but not enough to eliminate the problem. His analysis of the unguided protion of my last log is here:

A clear sinusoidal ripple at 5.54 seconds.

Waiting on a response from the vendor now.

[cotak]

What was the response?

[newbie alert]

On 10/12/2019 at 14:02, old_eyes said:

 

This graph tells me that your PA alignment in RA is going opposite to your DEC,  RA is dipping below the trendline and DEC above it.. how long are you leaving it to settle until you make the manual corrections,  are you choosing a star on the equator, DEC 0 ?

Have you any play in any axis if you give a wobble, are you balanced in all axis

Edited December 27, 2019 by newbie alert
Added info

[Starflyer]

On 13/12/2019 at 13:27, old_eyes said:

OzAndrewJ on Cloudy Nights analused my PHD2 Guidling Logs and diagnosed a bad SDE problem. Intensity was reduced by the beta firmware but not enough to eliminate the problem. His analysis of the unguided protion of my last log is here:

A clear sinusoidal ripple at 5.54 seconds.

Waiting on a response from the vendor now.

Any update on this @old_eyes?

[old_eyes]

Not really. Christmas, family and cloudy skies got in the way.

I did some further imaging runs on 16th, 17th, 20th and 29th. Some longer some shorter. Tests without guiding showed persistence of the frequency peak.

So far I have been using short focal length (500mm), and imaging widefield targets like M42, M31, NGC7000 and IC405. Given the typical seeing we have been getting, image plane not yet completely flat or orthogonal, and some focus issues, the results are not too bad.

I have turned down the PHD2 hysteresis to zero, set exposure at 4 seconds and cut RA aggression to 30%. With that setup guiding is at least not making matters worse. There is no sign of star elongation along the RA axis.

So I can at least do some imaging. However, what is acceptable at ~2arcsec/pixel will be a much bigger problem if I want to use a longer focal length.

The whole reason for the mount upgrade was to make sure that mount performance was not the limiting factor any more, so not willing to accept the oscillation.

Like all of us the vendor has been closed over the Christmas/New Year period. I will shortly be sending them the lastest data and hopefully we can together work out what to do.

[old_eyes]

@Starflyer - you can see an example of the early images I am generating here:

 

[Starflyer]

It's a great image and you must be pleased with the result.

It's hard to tell at that resolution but I think I can see a small left to right elongation, do you see the same thing?

If you're happy with the results you're getting then great.  At longer focal lengths, larger loads, the elongation due to SDE will show up even more. Essentially the PE of the mount is out of the manufactuer's quoted spec, SDE is a hardware defect, it will have been there from new and it won't go away through firmware updates.

It's an expensive piece of kit that promises a PE of < 0.3 arcsec, you're getting nowhere near that and if it were me I'd be insisting that it was exchanged.

[old_eyes]

On 05/01/2020 at 20:44, Starflyer said:

It's a great image and you must be pleased with the result.

It's hard to tell at that resolution but I think I can see a small left to right elongation, do you see the same thing?

If you're happy with the results you're getting then great.  At longer focal lengths, larger loads, the elongation due to SDE will show up even more. Essentially the PE of the mount is out of the manufactuer's quoted spec, SDE is a hardware defect, it will have been there from new and it won't go away through firmware updates.

It's an expensive piece of kit that promises a PE of < 0.3 arcsec, you're getting nowhere near that and if it were me I'd be insisting that it was exchanged.

Well spotted. There is a slight elongation to the right hand side. However, this is not the angle at which the oscillation is happening. That is North East to South West not West to East. I have not got the image plane completely flat or orthogonal yet, so that could be a factor.

I am picking it up again with teh vendor now that Christmas is over.

[cotak]

Good luck. My dealer just ignored me after a while.

[Adam J]

Looking at your images vs what I am seeing in the PHD chart the results done seem to align with the data. That kind of error should be very obvious in terms of star shape. Is there any chance that guiding is correct but that PHD is not correctly calibrated in the RA and so appearing to magnify the guide errors?

Adam 

[y_s_]

On 07/01/2020 at 08:50, old_eyes said:

I am picking it up again with teh vendor now that Christmas is over.

Gday @old_eyes what was the outcome? Did you manage to get it fixed? I have the same SDE problem with my CEM60EC, although not as large as yours and I am wondering if it can be rectified.

[old_eyes]

Weirdly, for operational purposes, it went away. Messing around with PhD2 settings, I got pretty good results by taking the aggression right down and using longish exposures (4-5 sec in my case).

Latest guide logs looked like this:

0.54 arcsec RMS in RA. According to meteoblue the atmospheric seeing at my location was 1.27-1.35 arcsec that night, so it was never going to be perfect.

The specific frequency of oscillation and the visible jumping of the guide star vanished.

Did the mount 'bed-in' in some way? Did I just hit on the right PHD2 settings? I will probably never know.

The mount is currently back with vendor due to a pier crash accident, but that is a completely different problem.

[Starflyer]

4 hours ago, old_eyes said:

Weirdly, for operational purposes, it went away. Messing around with PhD2 settings, I got pretty good results by taking the aggression right down and using longish exposures (4-5 sec in my case).

Latest guide logs looked like this:

0.54 arcsec RMS in RA. According to meteoblue the atmospheric seeing at my location was 1.27-1.35 arcsec that night, so it was never going to be perfect.

The specific frequency of oscillation and the visible jumping of the guide star vanished.

Did the mount 'bed-in' in some way? Did I just hit on the right PHD2 settings? I will probably never know.

The mount is currently back with vendor due to a pier crash accident, but that is a completely different problem.

4-5s guide exposures will be enough to hide the SDE problem. It will still be there, the mount hasn't bedded in and won't show in the image on short focal length scopes.  If you do a run at 0.5s and analyse the error then the SDE spike will still be there.

So long as you don't ever plan to try imaging at a longer focal length you'll be fine. It's not enough to give you oval stars at the moment, but SDE will smear stars at medium to long scopes.