Dithering (Dithering Timed-Out in APT).

[Rob 123]

Hello,

I took the next step in astrophotography.....dithering with APT & PHD2.

I think it went ok one night, had 3 out of 15 ditherings timed-out with the dithering setting time(40) that someone adviced(screenshot). I thought i just need some finetuning in the software. But the next time i went out to continue with dithering i kept getting timed-out. I kept trying several nights, but no luck. 1st i tried a litlle more and less unbalance, maybe that was on the edge because of the 3X time-out. So my scope is pointing south(on M13) and it's on the east side and made it a little more heavy there. After that i started to change the settings in APT: Dithering time out to 240s and 300s, dithering setting time to 15/40/60/80s and dithering start delay 5 and 10s. Still i had dithering time out on all images. I also noticed i had guiding programm on PHD and not on PHD2 so i set it on PHD2, that didn't help.

Setting up the mount/telescope is always the same:

* Put tripod/mount on the 3 markings on the floor (my house is blocking the view on the polar star, so i use drift-align in PHD2)
* Platesolve
* Adjust focus
* Force calibration & Drift align (and platesolve after mech adjusted or in the next step to my target)
* Platesolve M13 or load last image of M13 and blind solve GoTo

I have no idea why it worked and the next time it didn't.
Could it be that the focus on the OAG has to be better? I don't know if that has any influence.

Maybe you see something on the screenshot that isn't right(programm in APT is on PHD2 now).

So my plan is to set everything on default in APT dithering, same with PHD2 predictive PEC.

Do my platesolve, focus, force calibration & drift align and the guiding assistant and adopt it's recommendations(this i didn't do before).

Then i go to M13 and guide on the same star as before.

But i want to log it and i don't know if it's alway logging or do i need to check the box in Advanced setup under tab Global "Enable diagnostic image logging"? And how long should i log, make 5 images or 10 or more?

If i do something wrong or not in the right order please tell me.

My settings in PHD2 for the next time:

Thx in advance,

Rob

Imaging telescope: Celestron C8 edgeHD

Mount: Skywatcher EQ6-R
Imaging camera: Canon 5D MarkII(DAW-conversion)
Guiding: Celestron Off-Axis Guider
Guiding camera: ZWO ASI120MM mini
Focal reducer: Not this time.
Software: APT, Adobe Photoshop/GIMP, DeepSkyStacker, PHD2, Stellarium, ASCOM(POTHhub)

[Andy Galasso]

Hi Rob,

Could you please upload your Guide Log and Debug Log from a session where you had dither settle timeouts.   Log upload instructions: https://openphdguiding.org/getting-help/

Andy

[Brian Valente]

Rob what is your settling time in apt?

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[Rob 123]

Hi Andy,

i posted 3 Guide and Debug logs, wanted to post the logs of where i had 3 time outs out of 15 images(from the APT/PHD2 screenshot). I checked the RAW's date and time, 28 june 2019 1st one taken 00:14 and the last one 01:13.

So that must be the log that started the 27th, think i also added the on from the 29th.

And also a log from yesterday where i tried many things with the settings in APT and i think i also tried hysteresis algorithm from PHD2(normaly i use predictive PEC), but never had a dithering finished.

https://openphdguiding.org/logs/dl/PHD2_logs_3Nih.zip

Thx,

Rob

Op donderdag 4 juli 2019 20:57:22 UTC+2 schreef Andy Galasso:

[Rob 123]

Hi Brian,

the settling time was 40 when i had 3 time outs out of 15 images(you can see the settings in the APT/PHD2 screenshot).

Next day i tried with the same settings and never had a dithering finished. I tried different settle times, but no luck.

Rob

Op donderdag 4 juli 2019 21:04:34 UTC+2 schreef Brian Valente:

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[Rob 123]

Andy,

that is 00:14AM and 01:13AM timezone Amsterdam, Netherlands if you need it.

Rob

Op donderdag 4 juli 2019 20:57:22 UTC+2 schreef Andy Galasso:

Hi Rob,

[Brian Valente]

40 second at what pixel threshold?

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[Andy Galasso]

Hi Rob, thanks for sharing the logs. The settling failure is due to overly stringent settling criteria settings in APT.  You had it set to report settling done when the guide error stays below 0.7 px for at least 40 s. Your ordinary guide error was around 1.76 pixels (0.67 arc-seconds at 0.38 arc-seconds per pixel), so it is virtually impossible for the error to stay below 0.7 pixels for 40 seconds.  I'd recommend setting the settling parameters to 2.5 px and 8-10 seconds.

I notice a few other issues from the logs that can be easily fixed.

 1. set the camera to bin 2.  Create a new equipment profile (Connect Equipment > Manage Profiles > New using Wizard) and select binning 2.   This will alleviate may of the star loss errors and improve guiding.

 2. run the guiding assistant (Tools > Guiding Assistant) to get valid min-move settings for RA and dec -- your current settings were way too low and caused guiding to aggressively chase seeing.

 3. Connect your imaging apps including PHD2 directly to EQMOD ASCOM, no need to use POTH Hub (not necessarily a problem, but almost certainly unnecessary)

Andy

[Brian Valente]

Andy you kinda stole my thunder there :) but i was going to make the same observation - that is an extremely tough bar to meet for settling a dither. Personally i'd watch the dither settle and then pick an even more generous settle time - like 1-2 seconds. for my setup i usually do 1.6pix at 0 seconds, not recommending for you necessarily, but that is what works for me. 

Brian

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[Rob 123]

Hi Andy & Brian,

thanks for the explanation. I didn't touch the dithering stability, because i didn't exatctly know where to look for the value so i left it default.

Changed the values dither stability to 2.50 and dithering settle time to 10s.

1. I've made a new profile with binning 2. There's a thing i noticed from the last time i created a new profile. When PHD2 starts creating a dark library it all goes well till a point near the end.

At the end i see NOT RESPONDING in right top of the window, it's there very short and then after a couple of seconds the message finished is there. After this i went to "build dark library" and choose the option modify, no problems.

Then i did i created an entirely new dark library, also no problems. So maybe it's only when you create a new profile.

2. I will run the Guiding Assistant and apply the min-move settings for RA and DEC. I noticed the default DEC: agr = 100, is this ok? And what about the Backlash Compensation, leave it dissabled/off or not apply?

3. All set to EQMOD now.

Think i'm all set now, even the weatherforcast for tonight looks good. I let you know how it went.

Good to know that logging is always on, i guess i don't need to enable diagnostic image logging in the advanced setup.

Thx,

Rob

Op vrijdag 5 juli 2019 03:07:36 UTC+2 schreef Andy Galasso:

[Brian Valente]

Ho Rob

 

See below

 

Hi Andy & Brian,

 

thanks for the explanation. I didn't touch the dithering stability, because i didn't exatctly know where to look for the value so i left it default.

Changed the values dither stability to 2.50 and dithering settle time to 10s.

 

That still seems a bit excessive – just watch for your settling times, and if you find it’s taking too long, you can drop down the settle time appropriately

 

1. I've made a new profile with binning 2. There's a thing i noticed from the last time i created a new profile. When PHD2 starts creating a dark library it all goes well till a point near the end.

At the end i see NOT RESPONDING in right top of the window, it's there very short and then after a couple of seconds the message finished is there. After this i went to "build dark library" and choose the option modify, no problems.

Then i did i created an entirely new dark library, also no problems. So maybe it's only when you create a new profile.

 

 

2. I will run the Guiding Assistant and apply the min-move settings for RA and DEC. I noticed the default DEC: agr = 100, is this ok? And what about the Backlash Compensation, leave it dissabled/off or not apply?

 

DEC aggression at 100 is the default, that is fine

 

Regarding backlash compensation, if it’s already off I’d recommend leaving it off for now so we can see how DEC is behaving

 

3. All set to EQMOD now.

 

Think i'm all set now, even the weatherforcast for tonight looks good. I let you know how it went.

Good to know that logging is always on, i guess i don't need to enable diagnostic image logging in the advanced setup.

 

Awesome – looking forward to it

 

 

 

 

 

 

Thx,

 

Rob

Op vrijdag 5 juli 2019 03:07:36 UTC+2 schreef Andy Galasso:

Hi Rob, thanks for sharing the logs. The settling failure is due to overly stringent settling criteria settings in APT.  You had it set to report settling done when the guide error stays below 0.7 px for at least 40 s. Your ordinary guide error was around 1.76 pixels (0.67 arc-seconds at 0.38 arc-seconds per pixel), so it is virtually impossible for the error to stay below 0.7 pixels for 40 seconds.  I'd recommend setting the settling parameters to 2.5 px and 8-10 seconds.

I notice a few other issues from the logs that can be easily fixed.

 1. set the camera to bin 2.  Create a new equipment profile (Connect Equipment > Manage Profiles > New using Wizard) and select binning 2.   This will alleviate may of the star loss errors and improve guiding.

 2. run the guiding assistant (Tools > Guiding Assistant) to get valid min-move settings for RA and dec -- your current settings were way too low and caused guiding to aggressively chase seeing.

 3. Connect your imaging apps including PHD2 directly to EQMOD ASCOM, no need to use POTH Hub (not necessarily a problem, but almost certainly unnecessary)

Andy

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[Rob]

Hi Andy & Brian,

just finished 10 images(ISO1600-120s) on M13 with dithering and from start to finished dithering is just a couple of seconds.

I noticed the RA Osc is in the red numbers. Well i see that all the numbers are different when dithering, they go up and down.

Also the purple dots in the target window are....strange, but i guess that's dithering doing that.

What i was seeing before i dithered was a nice group of purple dots in the middle. Except when the mirror of the camera flipped, could see that in the graphs too.

I'll upload the logs tomorrow, just started a plan on M13(ISO800-600s) so i can have a look if it improves the image. I have some strange pattern in my images.

Rob

Op vrijdag 5 juli 2019 18:06:01 UTC+2 schreef Brian Valente:

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[Brian Valente]

Hi Rob

 

Sounds good – the sooner you can upload your logs the sooner we can give feedback

 

 

Thanks

 

Brian

 

portfolio https://www.brianvalentephotography.com/

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[Brian Valente]

Rob

regarding the "purple dots" - i think you are referring to the scatter plot?

if so, it looks like DEC is weighted in one direction - that usually means polar alignment could be improved, but i don't know, maybe you are guiding in one direction?

if you think something is happening around the dither you can choose the option to dither in RA only (in PHD under brain tab, Global settings)

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[Rob]

Hi Brain & Andy,

Brian the purple dots in the target window(with the bullseye) on the right top of my PHD2 screenshot. When i adjust the polar alignment(with drift align, have no view on polarstar at home) the dots are nicely grouped in the middle.

Now when i'm imaging they seem to move around and not in 1 direction, but they are still grouped.

Here's a screenshot from 2 months ago before i started dithering, also the RA Osc was always around 0,50:

But then again i don't know what PHD2 exactly does when dithering, if guiding is off when it starts dithering and switched on when dithering is finished that could explain a lot.

I'm a bit confused by the graphs and numbers atm, but thats why i went to you guys :).

Anyway here are the logs:

https://openphdguiding.org/logs/dl/PHD2_logs_FD69.zip

I started with a plan with 10 images (ISO1600/120s) on M13.

Started July 5th at 23:56 and the last image started at July 6th 00:17.

All went well and finished all 10 without any time out.

Next i started a plan (ISO800/600s), but could not finish(finished 8 images).....clouds. I think in the 3th image PHD2 lost the star for a moment.

Started July 6th 00:21 and the last image started 01:34.

All went well and finished all 8 without any time out.

So dithering works now :).

Now i need to see if dithering will remove that strange circular pattern of r,g and b dots/little stripes that has a center in the middle of the image and goes to the edges of the image.

Maybe ISO800/600s is to long and it will start showing that pattern and i need a shorter exposure time or maybe a lower ISO.

I didn't see or notice it in the ISO1600/120s after stacking and post processing.

Also i tried to find it in the lights/darks/bias/flats by level stretch, couldn't find it. Only after stacking in Deep Sky Stacker.

Thx, Rob

Op zaterdag 6 juli 2019 00:59:49 UTC+2 schreef Brian Valente:

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[Brian Valente]

Hi Rob

reviewing your guidelogs, things look pretty good. You had a nice calibration at the start and then you chose to recalibrate a couple times? once you get a good calibration, just stick with it

your overall RMS on segment 21 - your longest run at nearly 2 hours = was 0.7". RA and DEC were nearly identical at 0.54" and 0.53" , so you should have nice round stars.

if your images look good, i'd stick with this

looking more closely there is a fair bit of oscillations under your min move. it's possible if you tighten up your min move a little bit maybe 0.75 you might be able to squeak a little more tighter guiding, but i'd be happy with that right now

regarding this comment:

>>>Now i need to see if dithering will remove that strange circular pattern of r,g and b dots/little stripes that has a center in the middle of the image and goes to the edges of the image.

my guess is you are seeing "walking noise" - which is a pattern of noise due to insufficient dithering. your current dither is very minimal, especially for a DSLR. you are dithering less than 1 pixel on each dither, typically for DSLRs i hear 4-10 pixel dithers. 

others may have more experience with dithering and DSLRs, so they might offer some additional input on dithering. you might try increasing the PHD dither scale to 5-10? or look at your dither settings in your imaging app

Brian

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[Rob]

Hi Brian,

it's good to hear that it looks pretty good. I re-calibrated, because of drift-align. I don't know if any mechanical adjustment will influence the calibration, my best guess...software doesn't know i made changes so re-calibrate.

But if you say it don't have any influence i'll stick to 1 calibration next time.

Then i noticed something strange in Guiding Assistant. 1st 1 failed because the star was to close to the edge and later it failed and the graphic looked strange, had a bump in it(going down and the suddenly a bit horizontal and then down again).

Also at the end it failed to get to the guide star and resume guiding. Think i leave the guiding settings as it is, after i get some more experience i might start tweaking it a bit to get it better.

I did a quick stretch in DeepSkyStacker and with dithering it looks different. You mentioned dithering is less then 1 pixel, the dithering distance = 1 (in APT).

So now i got dithering working i guess the next step to increase the dithering distance. I go check what other people use with a DSLR, ask on a forum or i go for 8(somewhere between 5-10 like you said).

Here are 2 screenshots without and with dithering so you know what kinda problem it is and maybe seen it before or maybe you know what it is:

Thx for the good advice. Also using binning 2 was a good one, i think i also have more usable stars now(not sure) and that's nice when you use OAG.

Rob

Op zaterdag 6 juli 2019 17:53:16 UTC+2 schreef Brian Valente:

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