Jump to content


Photo

Guiding Issues

  • Please log in to reply
27 replies to this topic

#1 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 19 June 2013 - 11:34 AM

I'm still having problems when I try go guide.
My dec falls of the chart in PHD and I can't seem to get it to recover without stopping and restarting guiding. I've had this happen on both my attempts to guide

I've double checked by balance and it's real close.
I'm doing the All Star Polar Align
Guiding with an ST80 and the SSAG.
This is on a CGEM mount with a C9.25
Here is what my graph looks like. The jumps are where I stopped and started guiding again.

Any ideas what could be wrong?

Attached Files



#2 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 19 June 2013 - 11:36 AM

Here are my PHD Settings:

Attached Files



#3 Mike7Mak

Mike7Mak

    Apollo

  • *****
  • Posts: 1277
  • Joined: 07 Dec 2011
  • Loc: New York

Posted 19 June 2013 - 12:22 PM

Your 'Mx Dec' setting might be too low to overcome stiction/backlash in the dec axis. Increase it to 500 or even 1000 and see what happens. PHD only sends the correction pulse size needed so large set values don't really matter.

#4 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8101
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 19 June 2013 - 12:56 PM

Wow, that is pretty severe. looks like something is inhibiting the axis or the Dec guiding being stepped down or worse?.

My question is what does you calibration step(s) look like when you click the 'target' to start guiding. How many steps in each axis?

#5 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 19 June 2013 - 01:04 PM

I believe it took around 30 steps. to calibrate.

#6 Madratter

Madratter

    Fly Me to the Moon

  • *****
  • Posts: 6047
  • Joined: 14 Jan 2013

Posted 19 June 2013 - 01:09 PM

Wow. That is a really bad graph. First, I suspect that you have your guide rate set to a low fraction of the sidereal rate, perhaps something like .25. For now, up that to 1x sidereal. That in combination with poor polar alignment and a small max declination setting is torching any chance of keeping up with the drift on the declination axis. Bump that max declination setting up to something like 1000. If that doesn't do it, bump it up even more. When you get this under control, you can start backing that max declination setting and tracking rate setting back down some.

Not the issue here, but I wouldn't run with the RA aggressiveness at 101. I would pull that back to something like 95 so you aren't overshooting and porpoising. There does look to be some of that going on in the graph on the RA axis.

Although they say you can use just about any star for ASPA, some are definitely better than others. You want something reasonably close to the Celestial Equator and reasonably near the Meridian. Currently Spica would be a good choice in the early evening.

Make sure when doing your ASPA that you either defocus the stars you use for alignment by a considerable amount or use an illuminated reticle eyepiece to do your initial alignment. Also make sure you do a full 2+4 initial alignment.

#7 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8101
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 19 June 2013 - 01:11 PM

Change that to where you are getting 12 to 16 steps, it will depend a little on where you are pointing your scope but that a good ballpark to try for.

#8 jsines

jsines

    Mariner 2

  • *****
  • Posts: 255
  • Joined: 06 Sep 2011
  • Loc: Berkley. Michigan

Posted 19 June 2013 - 01:21 PM

Change that to where you are getting 12 to 16 steps, it will depend a little on where you are pointing your scope but that a good ballpark to try for.



Can you do this in the settings? I've just started autoguiding using PhD. I'm getting basically a flat graph, no problems from the start and nothing like the OP's graphs, but it's taking about 30 steps to calibrate. I'd like to shorten it to save on time if I could.

(sorry for the hijack)

#9 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 19 June 2013 - 01:24 PM

I suspect that you have your guide rate set to a low fraction of the sidereal rate, perhaps something like .25. For now, up that to 1x sidereal.


Is the guide rate you are referring to set on the hand controller? I see it listed as an option in the manual.

#10 Madratter

Madratter

    Fly Me to the Moon

  • *****
  • Posts: 6047
  • Joined: 14 Jan 2013

Posted 19 June 2013 - 03:18 PM

Change that to where you are getting 12 to 16 steps, it will depend a little on where you are pointing your scope but that a good ballpark to try for.



Can you do this in the settings? I've just started autoguiding using PhD. I'm getting basically a flat graph, no problems from the start and nothing like the OP's graphs, but it's taking about 30 steps to calibrate. I'd like to shorten it to save on time if I could.

(sorry for the hijack)


Yes. Change your calibration step size. You can go much bigger than the default. Just make sure your step size is smaller than the # of seconds for your exposure (so if you expose for 4 seconds, you better not go above 4000ms). I do tend to expose for 4 seconds. I use a calibration step size of 2500ms with my 50mm guider.

#11 Madratter

Madratter

    Fly Me to the Moon

  • *****
  • Posts: 6047
  • Joined: 14 Jan 2013

Posted 19 June 2013 - 03:19 PM

I suspect that you have your guide rate set to a low fraction of the sidereal rate, perhaps something like .25. For now, up that to 1x sidereal.


Is the guide rate you are referring to set on the hand controller? I see it listed as an option in the manual.


Yes it is. Or alternatively if you are running nexremote, you can change it in that as well (the value still gets stored in the controller).

#12 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8101
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 19 June 2013 - 03:24 PM

Can you do this in the settings?


yes, increase or decrease the number in the 'calibration step' in the brain icon functions ( the settings table should look somewhat like in the graphic above). increasing the number should decrease the number of steps it requires in the calibration. Of course the right number is any that gives you round stars at your exposure length.

There is a second party guide to PHD here, that might be useful.

.

#13 sparky123

sparky123

    Ranger 4

  • *****
  • Posts: 303
  • Joined: 14 Jun 2010
  • Loc: 41°N 96°W

Posted 19 June 2013 - 03:51 PM

i battled PHD when i didnt have the most current MC firmware installed....my graphs were all over the place similar to yours. I upgraded MC and HC firmware and on my very next attempt i was guiding and taking 10 minute exposures with no streaking at all

#14 Ron (Lubbock)

Ron (Lubbock)

    Messenger

  • -----
  • Posts: 428
  • Joined: 17 Aug 2012
  • Loc: West TX

Posted 19 June 2013 - 08:58 PM

What you appear to have is the "Dec. cogging" issue that plagues the CGEM. The characteristic sawtooth pattern is due to the Dec. motor ignoring small corrections from PhD. There is a bug in the motor control firmware that allows this problem to occur in the Dec. only. Celestron is working on a fix. Do a search on "CGEM motor cogging" on the mounts forum and you will find a long thread.

You can become a Celestron beta-tester and download a new version of the motor control firmware from the Celestron beta tester website (teamcelestron.com). Versions 31.15 and higher of the motor control firmware will eliminate the sawtooth. The bad news is that you will likely have to buy a couple of cables that run about $45 to update the software through the hand controller. I had the sawtooth problem as well, and it's gone now that I upgraded the MC firmware.

In the mean time, work on improving your polar alignment technique. With near-perfect polar alignment, the sawtooth will almost disappear. Also increase Max. Dec. to 1600 until you can upgrade the firmware. I recommend looking up drift alignment if you don't already know it. It's a good method to check if you did the All-Star correctly or not. I usually need to drift align even after All-Star. In order to get a sawtooth as bad as you are showing, polar alignment must have been off by quite a bit.

Good luck!

#15 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 19 June 2013 - 09:42 PM

Change your guide rate in the HC to 1.0x. Then, change your mx Dec to something high.. like 1-1500ms. Make sure your declination is balanced perfectly, cables attached, everything where it is gonna be when you image...

Finally, I was never happy with my CGEM and heavy weight. It performed really well when I got it below about <25#.

If you go to Craig Stark's website, go to his FAQ section. There is a tutorial in there called 'PHD for dummies' or something like that. Kind of explains everything.

Good luck!

#16 Ron (Lubbock)

Ron (Lubbock)

    Messenger

  • -----
  • Posts: 428
  • Joined: 17 Aug 2012
  • Loc: West TX

Posted 19 June 2013 - 10:41 PM

I take it you got rid of your CGEM, Raginar? The Dec. cogging fix was just done about a month ago, and they suddenly work a lot better for guiding. I don't know about 25 pounds plus load though- I think my imaging train is like 24 pounds.

#17 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 20 June 2013 - 07:48 AM

Thanks for all the great info! I'll try some of the settings tonight if it stays clear.

Sounds like I need to try the firmware upgrade too. I already have the cables necessary for the upgrade. I'll check into that after I get the settings a little closer.

My plan is to get an Sky-Watcher 80ed or 100ed for most of my imaging. That will make the load for the CGEM much lighter than it is now.

#18 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 20 June 2013 - 08:41 AM

Ron,

Yea, I don't have a CGEM anymore. That's interesting that the fix is done. Is it out of beta testing? Either way, what he is seeing is more than just cogging. I never had it that bad, even when I was near 37#.

Joe,

Try a focal reducer to reduce your focal length and make things easy too. Alternatively, you could get a mini-guider setup. There are numerous examples of them working C9.25s on Astrobin. I had great success with my C5/mini-guider on a CGEM. I think an ED80 would work good too :).

#19 Madratter

Madratter

    Fly Me to the Moon

  • *****
  • Posts: 6047
  • Joined: 14 Jan 2013

Posted 20 June 2013 - 10:13 AM

That sawtooth pattern was actually caused by him stopping and restarting guiding as stated in the original post.

#20 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8101
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 20 June 2013 - 11:10 AM

I think this can be an area of frustration. Guiding issues and then needing clear skies to try out remedy. IMO the good news is that you just need to learn your mount and guider setup one time 'all the way'. What matters where and how, and what the mount can do on a good night. The list of what can go wrong and how is huge, and if you are setting up from scratch each time there is that always possibility of human error(s) and batteries wearing out or connex wearing or cable issues. Patience and tenacity will win the day, this is the time in the saddle part where it starts getting clear all you don't know for certain. We all go through this with our gear and consider it one of those rights of passage.

#21 Ron (Lubbock)

Ron (Lubbock)

    Messenger

  • -----
  • Posts: 428
  • Joined: 17 Aug 2012
  • Loc: West TX

Posted 20 June 2013 - 11:57 AM

I did read that the OP had stopped and restarted guiding. However, there is no way he could get such declination drift unless his polar alignment was significantly off and the mount was also ignoring corrections in Dec. from Ph.D.
Those two factors point to Dec. cogging.

The reason the sawtooth did not happen on its own is that his max. Dec. was set to 200, which is generally too low to make it jump back to the setpoint on its own. I've witnessed my mount ignoring corrections of 800-1200 in Dec. from Ph.D., if you can believe that. Increase the Max Dec. to 1600, and you'll get some nice sawtoothing without stopping and restarting. :)

The beta firmware fixes are good enough that I'd suggest upgrading right away, rather than waiting for the public release. Any bugs left in the beta firmware are way insignificant compared to the dec. cogging. I've only managed to "break" the beta firmware by deliberately misaligning the scope by about a degree. It otherwise worked great in 8 or 9 imaging sessions last month. If not for the fix, I would have sold my CGEM already.

#22 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 21 June 2013 - 11:47 AM

I made some progress last night with my guiding. I've attached the PHD graph from last night. I'm guessing the first spike is the dec cogging problem. The 2nd one is where I stopped and started guiding again.

The calibration is occurring in about 12 steps.

This weekend I'm going to try to get the HC updated with the beta version of the software. Hopefully that will help some too.

The only thing I couldn't figure out was how to set the guide rate in the HC. I couldn't find it on the menu any where. Can someone point me in the right direction for that?

Attached Files



#23 woolbrig

woolbrig

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 01 Feb 2013
  • Loc: Bethalto, Illinois

Posted 21 June 2013 - 11:53 AM

New PHD Settings:

Attached Files



#24 fishonkevin

fishonkevin

    Surveyor 1

  • *****
  • Posts: 1767
  • Joined: 29 Apr 2007
  • Loc: Michigan

Posted 21 June 2013 - 12:58 PM

Guide Rate in HC = Tracking Rate/Speed ?? :question:

#25 Ron (Lubbock)

Ron (Lubbock)

    Messenger

  • -----
  • Posts: 428
  • Joined: 17 Aug 2012
  • Loc: West TX

Posted 21 June 2013 - 02:23 PM

I think the factory default guide rate is fine. I once looked it up, but don't remember how to get there in the menu. I would guess Menu -> scope setup is the right way to start.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics