Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

PHD2 guiding - settling time

  • Please log in to reply
11 replies to this topic

#1 georgian82

georgian82

    Viking 1

  • *****
  • topic starter
  • Posts: 580
  • Joined: 16 Jan 2016
  • Loc: Healdsburg, California

Posted 14 August 2019 - 01:12 AM

Hi guys,

 

What is the best way to determine the setting time in PHD2? I have mine set to 1.5 and 10 seconds and it constantly fails to settle. I obviously need to adjust the parameters, but by how much?

 

Thanks in advance,

 

Sebastian



#2 james7ca

james7ca

    Cosmos

  • *****
  • Posts: 7573
  • Joined: 21 May 2011
  • Loc: San Diego, CA

Posted 14 August 2019 - 02:10 AM

I guess you are dithering. IMO, dithering is a two edged sword, it can help to eliminate "walking noise" but it can also compromise your guiding.

 

Given a clear night with enough time to do the setup I use an A-P Mach1GTO mount that can deliver some really low RMS guide errors, but only if you allow the mount to settle for several minutes after each major move of the mount. Thus, IMO, any appreciable dither that is done frequently is just going to upset your guiding. Of course, some of this depends upon your image scale and I typically image at 0.75 arc seconds per pixel and I want my subs to show as little guiding error as possible. So, either dither less frequently, or settle longer, or be willing to toss some subs for guiding errors. I'd probably go for the less frequent approach and then keep your exposures fairly short in duration so that a too brief of a settling only affects a single sub among many.

 

But, of course, a better mount and/or a more careful adjustment of your PhD guiding parameters may help with the settling time. Unfortunately, PhD adjustments can be pretty variable depending upon your mount, its loading and balance, and the seeing conditions, so only you can determine how much to adjust the parameters. In my experience, however, even small adjustments can make significant differences and once you begin to get close you want to make only very small changes in the settings. And note, these setting can change from night to night based upon the seeing conditions and the location in which your mount is pointed (east/west, north/south, etc.).

 

Also, have you tried PhD's guiding assistant? It may not do better than pure user experience, but it might help set some bounds for a start.


  • georgian82 likes this

#3 jdupton

jdupton

    Vanguard

  • *****
  • Posts: 2095
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 14 August 2019 - 07:00 AM

Sebastian,

 

   I don't know what is "best" and it is probably different for everyone. Much will depend on your image scale and the average seeing at your site. I image (and guide) at an image scale of 0.482 "/px using 2 to 3 second guide exposures. I am very well polar aligned with PHD2 Log Viewer reporting an average drift rate of 0.02 "/min over a 3 to 4 hour session. My guiding is generally pretty smooth.

 

   I "high dither" every 4th frame and have my settling scale set to 2.0 px for one guide period (2 or 3 seconds). It takes my system an average of 3 to 4 guide exposures to report settled. Once settled, I don't see much effect afterwards. In other words, once the initial settling below 2 pixels, I do not see any further excursions larger than that in my system. (I also run guiding a pretty low aggressiveness with larger min move criteria -- Agg=40, MinMo=0.40 or larger.

 

   My reasoning for setting these values were that 1) the settling distance is about half my best case seeing at my site, 2) since I am oversampling, any settling is still well below my seeing level, and 3) since my mount shows smooth recovery from the dithers without overshooting and re-correcting. I do sometimes tweak them a little based on conditions for a given night but have found that these work well for my setup.

 

 

John


  • georgian82 likes this

#4 terry59

terry59

    Cosmos

  • *****
  • Posts: 9203
  • Joined: 18 Jul 2011
  • Loc: Colorado, USA

Posted 14 August 2019 - 07:08 AM

I use a small dither with 0.3 px and 5 seconds when using my CCD camera on the G11 and GM-8. Settling generally takes 2 to 6 seconds depending on the instantiation of each dither. I'm planning on using a medium dither with the CMOS camera but don't have enough sessions with it to have good data


Edited by terry59, 14 August 2019 - 07:12 AM.

  • georgian82 likes this

#5 billdan

billdan

    Mariner 2

  • -----
  • Posts: 247
  • Joined: 21 Feb 2012
  • Loc: SE Queensland

Posted 14 August 2019 - 07:42 AM

If you are dithering in DEC as well as RA, then settling time will depend on your DEC backlash response time.

RA will settle quickly as it either slows down or speeds up. DEC in some dither situations will have to change direction and that's where the settling time is increased. Of course you can work around this by dithering in RA only, but you reduce the benefit of dithering in this case.


  • georgian82 likes this

#6 pgs/sdg

pgs/sdg

    Messenger

  • *****
  • Posts: 429
  • Joined: 18 Jul 2014
  • Loc: 36°N, 92°W Ozark Mountains on the White River

Posted 14 August 2019 - 04:18 PM

Sebastian,

 

   I don't know what is "best" and it is probably different for everyone. Much will depend on your image scale and the average seeing at your site. I image (and guide) at an image scale of 0.482 "/px using 2 to 3 second guide exposures. I am very well polar aligned with PHD2 Log Viewer reporting an average drift rate of 0.02 "/min over a 3 to 4 hour session. My guiding is generally pretty smooth.

 

   I "high dither" every 4th frame and have my settling scale set to 2.0 px for one guide period (2 or 3 seconds). It takes my system an average of 3 to 4 guide exposures to report settled. Once settled, I don't see much effect afterwards. In other words, once the initial settling below 2 pixels, I do not see any further excursions larger than that in my system. (I also run guiding a pretty low aggressiveness with larger min move criteria -- Agg=40, MinMo=0.40 or larger.

 

   My reasoning for setting these values were that 1) the settling distance is about half my best case seeing at my site, 2) since I am oversampling, any settling is still well below my seeing level, and 3) since my mount shows smooth recovery from the dithers without overshooting and re-correcting. I do sometimes tweak them a little based on conditions for a given night but have found that these work well for my setup.

 

 

John

Is the above your settings for the HDX 110 or the Atlas?



#7 jdupton

jdupton

    Vanguard

  • *****
  • Posts: 2095
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 14 August 2019 - 04:24 PM

pgs/sdg,

 

   Those are the current settings I use for my HDX110.

 

   It has been about six years since I used the Atlas for imaging. I think I used higher aggressiveness with the Atlas. The MinMo settings were about the same, though. The Atlas didn't recover quite as well as the HDX110 after a dither and I think I disabled the Settle For x seconds and just took a hit on star eccentricity and FWHM.

 

 

John



#8 georgian82

georgian82

    Viking 1

  • *****
  • topic starter
  • Posts: 580
  • Joined: 16 Jan 2016
  • Loc: Healdsburg, California

Posted 15 August 2019 - 01:36 AM

I guess you are dithering. IMO, dithering is a two edged sword, it can help to eliminate "walking noise" but it can also compromise your guiding.

 

Given a clear night with enough time to do the setup I use an A-P Mach1GTO mount that can deliver some really low RMS guide errors, but only if you allow the mount to settle for several minutes after each major move of the mount. Thus, IMO, any appreciable dither that is done frequently is just going to upset your guiding. Of course, some of this depends upon your image scale and I typically image at 0.75 arc seconds per pixel and I want my subs to show as little guiding error as possible. So, either dither less frequently, or settle longer, or be willing to toss some subs for guiding errors. I'd probably go for the less frequent approach and then keep your exposures fairly short in duration so that a too brief of a settling only affects a single sub among many.

 

But, of course, a better mount and/or a more careful adjustment of your PhD guiding parameters may help with the settling time. Unfortunately, PhD adjustments can be pretty variable depending upon your mount, its loading and balance, and the seeing conditions, so only you can determine how much to adjust the parameters. In my experience, however, even small adjustments can make significant differences and once you begin to get close you want to make only very small changes in the settings. And note, these setting can change from night to night based upon the seeing conditions and the location in which your mount is pointed (east/west, north/south, etc.).

 

Also, have you tried PhD's guiding assistant? It may not do better than pure user experience, but it might help set some bounds for a start.

Yes, I am attempting to dither every frame to reduce walking noise which is putting my mount to the test. My guiding last session oscillated between 0.7-1.6" RMS and it never settled properly after dithering. I reviewed each sub and most look fine but I definitely lost a few in the process...

 

Thanks



#9 georgian82

georgian82

    Viking 1

  • *****
  • topic starter
  • Posts: 580
  • Joined: 16 Jan 2016
  • Loc: Healdsburg, California

Posted 15 August 2019 - 01:39 AM

Sebastian,

 

   I don't know what is "best" and it is probably different for everyone. Much will depend on your image scale and the average seeing at your site. I image (and guide) at an image scale of 0.482 "/px using 2 to 3 second guide exposures. I am very well polar aligned with PHD2 Log Viewer reporting an average drift rate of 0.02 "/min over a 3 to 4 hour session. My guiding is generally pretty smooth.

 

   I "high dither" every 4th frame and have my settling scale set to 2.0 px for one guide period (2 or 3 seconds). It takes my system an average of 3 to 4 guide exposures to report settled. Once settled, I don't see much effect afterwards. In other words, once the initial settling below 2 pixels, I do not see any further excursions larger than that in my system. (I also run guiding a pretty low aggressiveness with larger min move criteria -- Agg=40, MinMo=0.40 or larger.

 

   My reasoning for setting these values were that 1) the settling distance is about half my best case seeing at my site, 2) since I am oversampling, any settling is still well below my seeing level, and 3) since my mount shows smooth recovery from the dithers without overshooting and re-correcting. I do sometimes tweak them a little based on conditions for a given night but have found that these work well for my setup.

 

 

John

Hi John,

 

Thanks for the response. Do you mind elaborating a bit more how the image scale plays a role in the settling time? My image scale is 2.23"/px.

 

Thanks again



#10 georgian82

georgian82

    Viking 1

  • *****
  • topic starter
  • Posts: 580
  • Joined: 16 Jan 2016
  • Loc: Healdsburg, California

Posted 18 August 2019 - 04:57 PM

Hi guys,

What settings (if any) regarding dithering should be on or off in PHD2 so it doesn’t affect NINA?

Thanks

#11 rgsalinger

rgsalinger

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5251
  • Joined: 19 Feb 2007
  • Loc: Carlsbad Ca

Posted 18 August 2019 - 06:11 PM

Any imaging software that's intended for use in long exposure astro-photography has to have some criteria to determine whether or not the mount has settled sufficiently after a dither for the system to open the camera shutter. I've never noticed that frequent dithering affected my guiding (YMMV), but I've always set up my systems so that I'm "settled" when the guiding error is reduced to less .75 arc seconds.  That's some number of pixels, of course, and you arrive at that number using your image scale. If (NINA?) your imaging software for some reason can only handle a number of clock seconds then good luck to you. I cannot see that being very reliable particularly if you change aggression and or guiding cadence as you'd have to keep changing the number of seconds to match those changes. 

 

If your mount "never settled" then I'd be looking at the whole system to see why it's so unstable but again, using the criterion of pixels translated into arc seconds is the only way to get consistent images. I guess that this could happen, of course, if you have very very low aggression and at the same time long guiding exposures.


  • georgian82 likes this

#12 Stelios

Stelios

    Cosmos

  • *****
  • Moderators
  • Posts: 7967
  • Joined: 04 Oct 2003
  • Loc: West Hills, CA

Posted 19 August 2019 - 04:55 AM

I find it saves time to settle at a worse level than you typical guiding.

 

With my Mach1, I rarely have worse guiding than 0.7. But if I try to settle at 0.7 for 12 secs, it’ll take some time—first to reach that level and then consistently stay under. 

 

So I “settle” at 1.0 for 12 secs. Usually the marks are 1, 0.9, 0.8, 0.7–and imaging starts as the scope has settled, rather than be approaching settling.


  • georgian82 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics