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Polar aligned, poor tracking

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#1 lsintampa

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Posted 21 November 2020 - 07:11 PM

New at this, about a year now. 

 

I used sharpcap to polar align..  it seemed to work.  I'm using a AVX mount

 

Got it to "good" according to sharpcap.   Noticed that any slight adjustment when you get close was drastic.  Left a smidge would result in needing to go right a smidge.  North and south same.  So I figure if I got it to "good" that should be fine for tracking, right? 

 

Even just watching sharpcap without touching any adjustments the alignment adjustments would vary, but still say "good".

 

Started PHD2 and tried tracking after using APT to plate solve pleiades.  Tracking worked to some extent, but the errors were way off.  Graph was all over the place.

 

So how "good" does polar alignment need to be to get good tracking?  

 

I don't know how much better I could get PA using sharpcap..  would SPA in PHD2 be a better option?  Could my AVX be an issue?  IE too tight in RA or something else?

 

Very frustrated with both processes.  Can't do much DSO work without both being better than "good".



#2 AZ Maverick

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Posted 21 November 2020 - 07:17 PM

Hard to tell without knowing more info, but is sounds more like incorrect PHD2 settings than polar alignment if you got to 'Good' in SharpCap.

Can you attach the PHD2 guide log to your next post?



#3 kathyastro

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Posted 21 November 2020 - 07:22 PM

Lots of things could make the PHD2 graph go "all over the place".  Polar alignment could be one reason, though it would tend to make PHD2 do a lot of corrections in the same direction, rather than being all over the place.

 

Other possible reasons:

- guide camera image scale is inappropriate for the imaging camera's image scale;

- backlash in the mount;

- aggressiveness is set too high or too low;

- other PHD2 parameters need tweaking.



#4 jrcrilly

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Posted 21 November 2020 - 07:56 PM

I'd sort the tracking/guiding problem before focusing on polar alignment. Then, if I were going to trust a software PA I'd go with the PhD2 drift align routine. Too many potential errors with routines that look at only one point near the Pole.



#5 TelescopeGreg

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Posted 21 November 2020 - 08:21 PM

There are a lot of things that can cause an AVX to go "all over the place".  Balance is one.  Also the PHD2 settings, but I presume that you went through PHD2's Calibration routine, yes?  And it liked what it got?  When I was first starting (ok, so for the first 2 years), I never had PHD2 go through a calibration without finding something wrong.  Turned out the root cause was balance.  I tweaked it a bit, and all has been fine since.

 

But backing up a bit, the major cause of an AVX not cooperating is that it's carrying too much.  What do you have for a scope and camera on top, and what guider system (scope and camera)?



#6 fourfives

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Posted 21 November 2020 - 08:27 PM

few things I would check:

 

  • If your PA is under a minute in each direction I would think that isn't your issue.  
  • Make REALLY sure your scope/rig is completely balanced
  • Look for a cable snag - you never know
  • Wipe your calibration data in PHD2 and after your tracking a target with sidereal and focused....recalibrate.  Turn gain way up and do short exposures
  • Check your PHD2 settings and make sure your focal length and pixel scale are set correctly.  If you question it ....create a new profile.
  • Are you using eqmod/ascom  - did you check the RA and DEC rate under pulseGuide section
  • Unsure how many seconds you loop the guide camera....but if your under 3 seconds might want to increase it to 3 or 4 secs.

*These are things that i've learned for myself and my specific setup...and every ones setup is different.

 

 



#7 lsintampa

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Posted 21 November 2020 - 08:33 PM

This is all new to me....

 

I did find that my scope FL setting was off.... I just purchased the ZWO mini guide scope - it has a FL of 120mm the PHD setting was set to 240... not sure what effect that may have had.

 

I presume that PHD2 sets the camera settings correctly (pixel size, etc.) when you set it up - yes?  Using the ZWO ASI120 mini camera as my guide camera.

 

Using 72mm APO doublet as main scope and currently using Nikon D5300 for imaging camera.

 

How do you "wipe" your calibration data - and how do you "recalibrate"?

 

What other settings should I check?  There doesn't seem to be that many.  As to agressiveness - it is the default 75 - too high?  too low?  



#8 TelescopeGreg

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Posted 21 November 2020 - 09:20 PM

This is all new to me....

 

I did find that my scope FL setting was off.... I just purchased the ZWO mini guide scope - it has a FL of 120mm the PHD setting was set to 240... not sure what effect that may have had.

 

I presume that PHD2 sets the camera settings correctly (pixel size, etc.) when you set it up - yes?  Using the ZWO ASI120 mini camera as my guide camera.

 

Using 72mm APO doublet as main scope and currently using Nikon D5300 for imaging camera.

 

How do you "wipe" your calibration data - and how do you "recalibrate"?

 

What other settings should I check?  There doesn't seem to be that many.  As to agressiveness - it is the default 75 - too high?  too low?  

Re-Calibration is done by simply holding down the Shift key when you click the Guide icon.  That will replace the current calibration with a new one.  There are also choices in the menu system somewhere.

 

PHD2 can get the pixel size from the camera driver, and should be reporting what it got in the "brain" icon at the bottom. 

 

As for the rest of the settings, you can also run the Guiding Assistant (under the Tools menu at the top), where it will basically watch your mount's guiding and suggest changes to the settings to improve the overall performance.

 

If you can post a screen shot of a guiding session, we can learn a lot more about how the system is performing.  But overall, each AVX tends to have its own, um, "personality", with some better behaved than others.  You will need to play with the settings, both in PHD2 and in how you set up and balance (or purposely imbalance) your mount, to see what yours likes.  It will take some time and patience, and perhaps a bit of luck.



#9 alphatripleplus

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Posted 21 November 2020 - 09:20 PM

If your guidescope focal length is off by a factor of two, then PHD will be seeing the need for corrections twice as large as necessary (due to 2x focal length). That might explain why the guiding graph is going "all over the place". You also need to check in the "brain" advanced settings tabs whether your camera pixel size is set correctly - it should be read from the driver. 




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