Can Anybody Explain What Happened Here???

[StuartJPP]

First off I do not have dithering enabled, which would be a likely suspect...so two subs taken in succession...each a 5 minute sub with 5 seconds between them.

L_7042_ISO800_300s__22C.CR2.....Acquisition Began - 27/08/2016, 00:37:54.....Acquisition Ended - 27/08/2016, 00:42:58
L_7043_ISO800_300s__22C.CR2.....Acquisition Began - 27/08/2016, 00:43:03.....Acquisition Ended - 27/08/2016, 00:48:07

But flicking though the two images I get this "drift"...but there is no smearing of the stars. The drift must have happened between the acquisition of the images but it was only 5 seconds...The PHD2 graph for this period in time is pretty flat as well...I confirmed that the clock on the camera and the PC are synchronised.

There are a few instances of these...scattered randomly through the subs with varying amounts of "drift", but no smeared subs.

If there is a cable snagging (I had a dew heater cable that was dangling) and a sudden jerk of it, but that should show up either on the guide graph or the subs surely? And they always correct themselves in the 5 second between subs?

Canon 6D tethered to APT, PHD2 and Avalon StarGo...

Even if dithering was enabled or there is a bug in APT, surely it can't dither that quickly?

 

Any thoughts?

 

Flicking between L_7042_ISO800_300s__22C.CR2 and L_7043_ISO800_300s__22C.CR2

 

The guide graph covering the 10 minutes:

[Thalestris24]

Hmm... Does look like a dithering movement but can't be with dithering off... I believe APT can dither independent of PHD2?* though I've only ever dithered from APT via PHD2 and with fast restore set in PHD2. Could something else be moving the mount? Eqmod? I guess you should be able to get to the bottom of it by closely monitoring exposures  

Louise

* or is it PHD2 or something else dithering directly? 

[StuartJPP]

Louise, I can only believe that something is moving the mount between exposures...I will investigate APT (the plan was definitely set to "Don't Dither This Plan"), however I stopped the plan every now and then to check focus...but not between these two subs.

There are 3 possible sources of dithering...PHD, APT or the mount itself so I will have to eliminate each one. As I say though it is random, there can be a string of 10 subs with no movement and then 3 come along like buses...

StarGo doesn't necessarily know when an exposure has started or not as it is out of the loop. I can try an intervalometer next clear night to see if it is connected to APT/PHD2 because with an intervalometer PHD2 is non the wiser as to when exposures are being done...

 

[Thalestris24]

1 minute ago, StuartJPP said:

Louise, I can only believe that something is moving the mount between exposures...I will investigate APT (the plan was definitely set to "Don't Dither This Plan"), however I stopped the plan every now and then to check focus...but not between these two subs.

There are 3 possible sources of dithering...PHD, APT or the mount itself so I will have to eliminate each one. As I say though it is random, there can be a string of 10 subs with no movement and then 3 come along like buses...

StarGo doesn't necessarily know when an exposure has started or not as it is out of the loop. I can try an intervalometer next clear night to see if it is connected to APT/PHD2 because with an intervalometer PHD2 is non the wiser as to when exposures are being done...

 

Your stars look nice and round so I guess it must be a controlled movement. I'm sure there'll be an 'aha' moment when you fathom it! Good luck!

Louise

[almcl]

Not sure I can add anything to this but the image is in Cepheus (I think) and the movement is all in RA?

If I've got that right, it seems tracking is stopping (or speeding up - can't get my brain around that at the moment) between subs, yet there's no sign of this on the guide graph (I'd kill for a graph that good, BTW). 

There are some DEC spikes (very small and assuming red is DEC?) but these are only about half a pixel where as the image appears to move about a dozen pixels.  Strange.

[StuartJPP]

5 minutes ago, almcl said:

Not sure I can add anything to this but the image is in Cepheus (I think) and the movement is all in RA?

If I've got that right, it seems tracking is stopping (or speeding up - can't get my brain around that at the moment) between subs, yet there's no sign of this on the guide graph (I'd kill for a graph that good, BTW). 

There are some DEC spikes (very small and assuming red is DEC?) but these are only about half a pixel where as the image appears to move about a dozen pixels.  Strange.

I think the majority of the movement is in RA, but I will have to confirm that. And yes you are correct, it is taken in and around Cepheus.

Seeing wasn't great on the night with some thin cloud passing occasionally, but that will not cause this...the guide star was not lost at all, even though I couldn't see stars for a period.

I am suspecting some random inter-sub command to the mount to slew, at least I am getting dithering for free Seriously though I would prefer to find out what the issue is and then introduce dither properly...so the investigation will continue!

 

[ollypenrice]

It has to be a dither-like command. In my opinion software does what it likes so I'd guess it is doing some kind of univited dither...

Olly

[michaelmorris]

It could be worth posting issue this on the APT yahoo forum.

 

[Whirlwind]

I might sound really dense here because I don't know PHD2 or APT at all...

But looking at your Section header in your log viewer it does say "Dither = both axes, Dither Scale = 1.000..." which would imply your dithering is still on for some reason.  Otherwise I would have expected it to have said "Neither axis"; or "dither scale =0.000" (or both)

 

[ChrisLX200]

Could it (PHD) have flipped from one guidestar to another nearby?

ChrisH

[StuartJPP]

14 hours ago, ollypenrice said:

It has to be a dither-like command. In my opinion software does what it likes so I'd guess it is doing some kind of univited dither...

Olly

I write software Olly so yes I see where you are coming from

 

3 hours ago, michaelmorris said:

It could be worth posting issue this on the APT yahoo forum.

 

I might go down that route, will try the next clear night to isolate which is more likely the culprit as at this point there are just too many unknowns.

 

2 hours ago, Whirlwind said:

I might sound really dense here because I don't know PHD2 or APT at all...

But looking at your Section header in your log viewer it does say "Dither = both axes, Dither Scale = 1.000..." which would imply your dithering is still on for some reason.  Otherwise I would have expected it to have said "Neither axis"; or "dither scale =0.000" (or both)

 

Well spotted, normally PHD2 is instructed to dither by the program taking the images (in this case APT)...I will read up on how they all operate together...1st step is to disable dithering in PHD2 as well as APT (it is already disabled in APT)...

 

2 hours ago, ChrisLX200 said:

Could it (PHD) have flipped from one guidestar to another nearby?

ChrisH

Could be, but the chances of it happening between subs? Not sure what the graph would look like if it did?

 

Thanks for the comments everyone...all helpful in trying to isolate the issue...

 

 

[StuartJPP]

Right then I think I might have found the issue...I had recently noticed on my M-Zero that if I didn't plug in the hand controller the motors would very infrequently "dither"...as though a button on the hand controller was pressed quickly.

So anyway I think what was happening was that the keypad routine in the StarGo was in effect treating the keys as "floating" so that when the keypad was unplugged there was the slight chance of the keypad being erroneously being read as being pressed. With the keypad and cable plugged in the capacitance of the cable was enough to prevent it from happening...

SO I think that what was happening was that when downloading the images from the camera, i.e. heavy USB traffic, interfered with the keypad and caused the StarGo to nudge slightly during that USB traffic and and hence it only nudged between subs.

I have upgraded everything to the latest StarGo version and I can confirm that everything seems to be working properly...I had a bit of a mishap updating the StarGo controller...it failed at 94%, but luckily I managed to recover it. I think my USB power bank decided there was not enough current being drawn and so conveniently went into power-down mode and turned off just as it was about to finish

Anyway, after some testing on a partly cloudy Friday night I managed to get 45 minutes of consecutive subs with no drift between the 5 minute subs. The subs are quite rubbish as seeing was terrible but I wanted to test the new firmware. I generally don't like upgrading firmware because if it ain't broke and all that...plus look what happened, it failed at 94% and for a while I had a brick.

 

Moral of the story is to keep your firmware updated!

 

So here's the result from the 1st and 8th sub, (45 minutes) there still a slight bit of drift but I can live with that, now I need to introduce intentional dithering: