Star trails-Doubled stars

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Wael Omar

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Oct 8, 2021, 9:34:26 PM10/8/21
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Hello,
Last night , My imaging was normal and tracking was acceptable but after 3 hours from the start, I noticed that the images start to have some trails then they convert to something like doubled stars in my image. I thought there was something with my guiding scope but it was fixed and not loose , the guiding graph looks good and polar alignment too..I used skywatcher EQ 35 pro with Redcat 51 and guiding scope zwo 120mm.
I attached some of the images i have during this session, also this is my guide log:
Thank you.


bw_msgboard

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Oct 9, 2021, 11:11:24 AM10/9/21
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Well, this is pretty bad.  For starters, you weren't guiding at all from 23:02 until 01:08 because you allowed PHD2 to select a hot pixel.  That happened because you haven't configured it properly to help distinguish between sensor noise and real stars.  Please read about how to fix this in the trouble-shooting section of the manual - look for the topic on Hot-pixel and star-selection problems.  If the timestamps of your images are included in the filenames you sent, it looks like all of these sample images were taken during that timeframe.
 
Beyond that, you've got some mechanical problems with the guide scope assembly and probably the cables.  Your log is full of these kinds of abrupt shifts of the guide star (RA in red):
 
 
 
This can come from various sources.  If you're using one of the flimsy stalk-mounted finder-scopes, those are common problem areas.  These large, image-destroying guide star excursions correspond to shifts of the guide camera by less than 5 microns - 10% of the thickness of a human hair.  Because they are both abrupt and large, they can't be guided out effectively.  They can also be caused by cables that are snagging or dragging as they move over stationary parts of the mount or surfaces around the mount.  If you have cable ties or ribbed cable guides, those have small projections that will briefly catch then release as they slide over a surface. 
 
Good luck,
Bruce

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Wael Omar
Sent: Friday, October 08, 2021 6:34 PM
To: open-phd...@googlegroups.com
Subject: [open-phd-guiding] Star trails-Doubled stars

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Wael Omar

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Oct 10, 2021, 11:25:19 PM10/10/21
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Hello Bruce;
I'd like to say I am really impressed by how my Guiding become very good after I followed your advice for creating  Bad pixels map.
I renewed the dark library and also create bad pixel map as stated in : https://openphdguiding.org/man/Darks_BadPixel_Maps.htm
I see that the curves become so smooth and straight , only a few peaks come up and down every minute but this is the best guiding curve I have ever had since starting this hobby.
The clouds came that night to ruin everything again but after midnight things became clear but I noted that around 00:36 , 00:46 and 00:53 am  there were abrupt changes in the guiding curves . Don't know why! 
This is the guiding log for that night::
Tonight unfortunately I didn't get the same straight line guiding curve, I rebuilt the dark library and Bad pixel map but I found this time that the bad pixels are not shown even when I check " show defective pixels" and change the aggressiveness...it doesn't show up at all.
I tried to add what I saw as a bad pixel manually but it can't be added because the images keep changing in location of the pixels !
I started guiding after that but the curves returned back again to have noisy peaks in both RA and Dec. I could not get the smooth straight l8ne again.
This is the guiding log of tonight:
Thank you.


To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/F4B75F7456964252B6CE38245D28F9CA%40HomeDesktop.
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Brian Valente

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Oct 10, 2021, 11:50:58 PM10/10/21
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Hi Wael

It looks to me like you have solved your "guiding on a hot pixel" challenge.

Looking at your guiding performance, what Bruce mentioned is still happening:

>>>you've got some mechanical problems with the guide scope assembly and probably the cables.  Your log is full of these kinds of abrupt shifts of the guide star:

What does your guiding setup look like?


Beyond that, here are a few more observations:

- after midnight it does appear your guiding accuracy was diminished, but comparing before midnight and after, it was only .2" difference. Looking at the variable SNR in your guidestar after midnight, i'm guessing this was more seeing related than performance if your guiding. In addition your subsequence 46minute session actually improve to 1.26" overall RMS, so guiding subsequently was better than before. Chalk it up to seeing conditions

- Your calibration does not look good. You had a message your guide rates were questionable, not sure if you ignored that? you should re-do your calibration so the guide rates look comparable between DEC and RA. I think this is one of the primary limitations to your current guiding. Look at how few steps RA (in blue) took vs DEC, for the same guide pulses:

image.png

These should be much more similar to each other. You should re-do your guiding until they better match. and investigate your guide speeds to make sure these are correct. Make sure you are calibrating at the intersection of meridian and celestial equator (you can use the drift align tool to slew to that sky position if that helps you).

- Your guiding results may appear to be wavy, and bouncing back and forth, but this is because your min move limits are high enough to allow it. You should consider running the guiding assistant and following its recommenations. Your guide camera image scale is very rough at 6.45"/pix, and you are guiding around .15" per pixel. Getting your RA rate up should improve things on the RA. 

- Your mount's periodic error is still extremely high, 22" at 470 seconds:
image.png

you might consider using PPEC algorithm for RA, with the period set to 470 seconds and disable auto adjust period. That may help tame that


Brian

Wael Omar

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Oct 22, 2021, 12:57:11 AM10/22/21
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Hello Brian,
Sorry for the late reply but i was looking for clear skies, My guiding setup has ZWO mini guide scope ( Diameter: 30 mm. Focal Length: 120 mm. Weight (include guider ring and dovetail): 250 g. Back Focus: adjustable,（0~20 mm）. Focuser Type: front part focuser.) It is mounted on Redcat 51 by saddle plate (Attached photo No.1).

I tried to calibrate near the intersection of Celestial equator and meridian but i have the same message as before that my  calibration is questionable, i run the guiding assistant and one of the recommendation is to decrease the  Min mov for RA to be .11 instead of 0.18 and i applied it.

I had the same problem appeared again for double stars but not on all frame only few one like in this link:

But tonight the problem getting worse and really bad to almost all frames , i started the night by check all mechanical assembly of all parts and i fixed the guide scope in position firmly, Cables were straight and free from any kinks or snags ,  also check the guiding performance and it was acceptable but starting from 02:15 am until 04:26 am , the images show very rough drifting and bouncing in positions.
These are the images :
This is the guide log for tonight:
One thing i didnt carry out , PPEC for RA , i'll try to do it tomorrow to find out if this solves the problem.

Regards,
Wael






1.jpg

David Kerber

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Oct 22, 2021, 6:20:44 AM10/22/21
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I have seen the doubled stars in my rig when i had backlash compensation
enabled in the mount. It was causing oscillations between two extremes
in dec, causing every star to be doubled in the dec direction.
> image.png
>
> These should be much more similar to each other. You should re-do
> your guiding until they better match. and investigate your guide
> speeds to make sure these are correct. Make sure you are
> calibrating at the intersection of meridian and celestial equator
> (you can use the drift align tool to slew to that sky position if
> that helps you).
>
> - Your guiding results may appear to be wavy, and bouncing back
> and forth, but this is because your min move limits are high
> enough to allow it. You should consider running the guiding
> assistant and following its recommenations. Your guide camera
> image scale is very rough at 6.45"/pix, and you are guiding around
> .15" per pixel. Getting your RA rate up should improve things on
> the RA.
>
> - Your mount's periodic error is still extremely high, 22" at 470
> seconds:
> This can come from various sources.  If you're using one
> of the flimsy stalk-mounted finder-scopes, those are
> common problem areas.  These large, image-destroying guide
> star excursions correspond to shifts of the guide camera
> by less than 5 microns - 10% of the thickness of a human
> hair. Because they are both abrupt and large, they can't
> be guided out effectively. They can also be caused by
> cables that are snagging or dragging as they move over
> stationary parts of the mount or surfaces around the
> mount.  If you have cable ties or ribbed cable guides,
> those have small projections that will briefly catch then
> release as they slide over a surface.
> Good luck,
> Bruce
>
> ------------------------------------------------------------------------
> *From:* open-phd...@googlegroups.com
> [mailto:open-phd...@googlegroups.com] *On Behalf Of
> *Wael Omar
> *Sent:* Friday, October 08, 2021 6:34 PM
> *To:* open-phd...@googlegroups.com
> *Subject:* [open-phd-guiding] Star trails-Doubled stars
>
> Hello,
> Last night , My imaging was normal and tracking was
> acceptable but after 3 hours from the start, I noticed
> that the images start to have some trails then they
> convert to something like doubled stars in my image. I
> thought there was something with my guiding scope but it
> was fixed and not loose , the guiding graph looks good and
> polar alignment too..I used skywatcher EQ 35 pro with
> Redcat 51 and guiding scope zwo 120mm.
> I attached some of the images i have during this session,
> also this is my guide log:
> https://openphdguiding.org/logs/dl/PHD2_logs_oXQJ.zip
> Thank you.
>
> 2021-10-08_23-00-14_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/1bt8NIUwhBHfVwwdkp3ZhhVIF8QN4DTTp/view?usp=drive_web>
> 2021-10-08_23-05-15_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/15Yl6VYc7QNY0dAfGU8iVsx6BsdRzFeAC/view?usp=drive_web>
> 2021-10-08_23-10-16_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/1vk6-PLX5lDGdp9a97Q0263TOFjZdYytH/view?usp=drive_web>
> 2021-10-09_00-40-39_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/1fYJteHYrZKjVrKOcEjj1NZ0pTCfNzPOq/view?usp=drive_web>
> 2021-10-09_01-00-43_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/1-iGDOxPOF7D5LfdIt4uGEgPDnWgO0eH7/view?usp=drive_web>
> 2021-10-09_01-05-44_O_-10.00_300.00s_2x2IC 1805...
> <https://drive.google.com/file/d/1sbbVVsjXHVW5LdoFpoIo0RjSsuS-AYuW/view?usp=drive_web>
>
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>
>
> --
> Brian
>
>
>
> Brian Valente
> portfolio brianvalentephotography.com
> <http://brianvalentephotography.com>
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mj.w...@gmail.com

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Oct 22, 2021, 9:02:26 AM10/22/21
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Hi Wael

Not an expert, but I see in your 21st Oct that you didn't Calibrate.

A shame, because it was using the 22:21 Cal from the 12th October, which was awful.

That Cal had 22 steps of Dec Backlash.

As a result the guiderates calculated by that Cal were  RA = 11.4"/s    Dec = 5.9"/s;     for a mount setting of 9.0 a-s/s

So Dec rate half what it should be.

You MUST clear Dec Backlash before Calibrating !

And that much Dec Backlash could surely be reduced by worm adjustment.

RA PE was about 80arcsecs on a unguided run at 19:24 on the 12th, that's pretty poor.

Until you adjust the mount adjusted to get Calibrations without warning messages, you will not get consistent guiding.

Here's what the experts about setting up for a Cal:

1.  Make sure the scope is well-balanced in Dec.  When you release the clutches, it shouldn't start moving around on its own.
2.  Slew to a position near Dec = 0 and pointing well above the horizon.
3.  Clear the Dec backlash manually.  Start PHD2 looping camera exposures, then use the hand-controller to manually move the scope north ('up' button) until you can see the stars in the display moving.
4.  Then start the PHD2 calibration and let it complete.  It's important to get a calibration that doesn't trigger any warnings.

Michael
Wiltshire UK

Wael Omar

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Oct 23, 2021, 5:51:54 AM10/23/21
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Hello ;
Thank you Michael for your advice.
I am sure that my mount is balanced and scope is balanced with counter weight in Ra and also scope does not rotate in Dec. I redo the calibration again 3 times as what you described in the email below  last night but it gives the same result. I think it relates to mechanical issues in my mount gears.
One thing is that I examined all my images that have trails or doubled stars then I opened my guide log and tried to find what happened exactly at the time of those defected images, I found that each time the "settings failed" in PHD guide curve" attached image" this resulted in trails or doubled stars. I don't actually know what "Setting failed " means , if somebody helps I'll appreciate this.

PHG log.jpg
PHG log.jpg

mj.w...@gmail.com

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Oct 23, 2021, 7:49:18 AM10/23/21
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Hi Wael

That message actually reads SETTLING, not SETTING.

After a Dither, Settling Time allows the guiding to catch up with the new guiding position.

If your mount has a lot of backlash, the mount may not have Settled in the time your software has allowed.

Michael
Wiltshire UK

Wes Atchison

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Oct 23, 2021, 7:54:59 AM10/23/21
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Try turning off dither.  Looks like you have Dither turned on and the settings are not allowing enough time for PHD2 to settle before the imaging camera starts a new capture.  I would suggest you turn off Dither and see if you problem goes away.  If that works the play with the dither adjustments to allow enough settling time.  There have been several Threads recently about Dither settings.

Good Luck,

Wes

bw_msgboard

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Oct 23, 2021, 6:32:27 PM10/23/21
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If you would upload your latest log files, including one that has a calibration, we would be able to give you more specific help.  It's almost a certainty that your finder-scope guiding arrangement and its very coarse image scale is causing huge excursions of the guide star - nothing to do with guiding.
 
 
Bruce

From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Wael Omar
Sent: Saturday, October 23, 2021 2:52 AM
To: open-phd...@googlegroups.com
Subject: Re: [open-phd-guiding] Star trails-Doubled stars

PHG log.jpg

Wael Omar

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Nov 1, 2021, 3:26:12 PM11/1/21
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Hello Michael , Wes and Bruce.
Thank you all for your follow up and advice .
Here it's too cloudy and i only had few hours to test and have findings so here is what i ended up with :
1- The finder scope was fixed tight yo the saddle plate but the saddle plate itself is loosing with time so I had to fix it every night or even 2 times per night as the mount slewed overnight.
2- I found that many of star trails in my photos were due to small clouds that pop up in range of the finderscope and make the guide star disappear. that was very clear in my images that small part in the image was blown out because of clouds.
3- I needed to dither so I could not turn it off but I increased the settling time from 15 seconds to 40 and then 50. Of course I lost precious time of imaging but the results were very very good and only 2 or 3 images over all the night had star trails.
This is my last guide logs:



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mj.w...@gmail.com

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Nov 2, 2021, 12:39:32 PM11/2/21
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Hi Wael

Your 28th October last run showed  Dec errors were well controlled, Dec = 0.59 arcsecs.

But RA error was twice that,  RA = 1.38arcsecs.

Which means elongated stars.

I'm still seeing the same poor Calibrations as weeks ago.

Your 28th October Cal had 30 steps of Dec Backlash.

PHD2 can accommodate a few steps in it's Cal, but 30 steps seriously distorts the measurement of the guiderates.

In this case, the mount is set to    RA Guide Speed = 9.0 a-s/s,    Dec Guide Speed = 9.0 a-s/s,

But after the Cal the calculated rates were   Norm rates RA = 9.7"/s,   Dec = 5.4"/s

So Dec rate was half the RA rate.

Resulting in a warning message     Last Cal Issue = Rates

You can't keep ignoring these Cal messages and expect good guiding.

Michael
Wiltshire UK
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