Calibration was too far from equotor, calibration is needed error

[Sathya Venkataraman]

I am new this PHD2 guiding. 2 days ago I was getting this error. Not sure what to do. Los uploaded to https://openphdguiding.org/logs/dl/PHD2_logs_DLgz.zip

Please let me know.

Thanks.

VSN.

[Ken Self]

You performed your calibration at a declination of almost 70 degrees. At this location the guide star moves only a small distance in RA for a given pulse length. At the pole (90 degrees) it does not move at all. This causes calibrations near the pole to be unreliable so PHD2 issues an error

What you should do is to calibrate nearer to declination 0 for a more accurate calibration. Then move to your target. As long as the "Auto restore calibration" and "Use Dec compensation" options are ticked then wherever your target is, PHD2 will adjust the RA guide adjustments to suit the declination of the target.

https://openphdguiding.org/manual/?section=Advanced_settings.htm#Guiding_Tab

[Sathya Venkataraman]

Hi. 

Thanks for getting back. You mean set the mount to Zero position and do the calibration? Right? Just fyi my mount is iOptron GEM25.

[Ken Self]

No. As I understand it the iOptron Zero position is pointing at the pole which is declination 90 and at right angles to where you should be calibrating.

You need to slew to a declination close to 0 degrees aka the celestial equator

[Sathya Venkataraman]

how do I point to celestial equator? Is there an object that I tell the mount to go to?  Here is what I tried, I manually slewed 0 dec. It was pointing to my fence :-(  I don't think this is right. Also for guiding I am not using ST-4 but using ASCOM. Just fyi. 

[Ken Self]

If ou are slewing manually first slew to dec 0. As you found the scope will be horizontal. Then slew in RA to point upwards. I can't give you an object because the stars rotate in RA across the sky through the night. You could use Stellarium or Carte du Ciel to find a suitable star, get its coordinates and slew to that. You don't need to be exactly on dec 0. As long as you are within +/- 20 degrees that should be ok

[mj.w...@gmail.com]

Hi Sathya

I'm not one of the PHD2 experts.

Are you located north or south of the equator?

Roughly speaking, Dec=0 is where the sun will be a midday, if you can visualise that?

If you're south of the equator, that will be to the north, not south.

However, if that is pointing at a fence, then as Ken said, slew east or west in RA to clear the fence and then start PHD2 looping stars.

If there aren't any stars, then a very slow move in RA should bring stars into the view.

Now make some small moves north until the stars move, to clear Dec Backlash.

Now you can Calibrate.

Michael

Wiltshire UK

[Sathya Venkataraman]

Thank you. I am in California. I'll try moving the mount to horizontal position and point my scope over head and see if that works.  

[mj.w...@gmail.com]

I don't understand that reply Sathya.

From pointing at Polaris, don't move the mount to a horizontal position, leave the tripod where it was. 

And don't rotate the telescope overhead, point it to where I said, pointing south to where the sun would be at midday.

Which is approximately Dec =0.

Your handset will tell you when you at at Dec =0

Michael

Wiltshire UK

[Chuck Koos]

Non-expert here, but I've found this to work. It eliminates having to think, something I value.

After doing your polar alignment and star alignment, go to the tools menu in PHD2. Select "Drift Alignment". A box will pop up showing you where your scope is pointing, and also were it needs to point. Hit the "Slew" button. The scope will now slew to where you need to be pointing for calibration. After the scope finishes slewing, exit the drift alignment tool. Now perform the calibration. 

-chuck-

[Sathya Venkataraman]

Hi Michael, 

I wasn't planing to move the tripod. it will be pointing to Polaris. 

Here is what I understand.  let me know if anything wrong. sorry I am very new to all this and may be asking silly questions. 

1. First I set to Zero position (90 dec) and do polar alignment.  

2. Slew to Dec 0 manually using the hand control.Now the scope is pointing to my fence.  I think right now, the sun is at mid day is close to overhead for me. so that is not right place to point. If I understand, you want me to point to some star in south that is lower. right ? 

Thanks, 

VSN.

[Sathya Venkataraman]

Thanks you. I'll try that. 

[Geof Lewis]

FWIW, that's the method I use too....👍

Cheers,

Geof

---

From: 'Chuck Koos' via Open PHD Guiding <open-phd...@googlegroups.com>
Sent: 05 May 2021 23:55
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Re: Calibration was too far from equotor, calibration is needed error

 

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[Chuck Koos]

I should have mentioned that this doesn't work with a ST-4 only connection. PHD2 doesn't know where the scope is pointing in that case because scope position information isn't provided via ST-4. So you can't use this technique until you have a USB/Ascom connection on your mount.

[Brian Valente]

>>> until you have a USB/Ascom connection on your mount.

the ASCOM is really the important part - you don't have to specifically have a USB connection. Ethernet or serial or whatever connection can be used

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[Sathya Venkataraman]

Thanks. I am using ASCOMM usb setup only. No ST4. I'll try to tonight.

[Jim Pollard]

Just a couple pages down in the link you'll see a picture that shows the correct position for the telescope for calibration.

Hope this helps.

Jim

https://openphdguiding.org/man-dev/Tutorials.htm

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[mj.w...@gmail.com]

Hi Santhya.

Apologies, I wasn't making enough compensation for your location compared to mine.

California is a long piece of real estate, but from San Francisco, at noon the sun is way up high as you said, about 70 degrees above the earth's horizon, at about Dec = 15

So Dec = 0 is about 55 degrees above your horizon.

My bad

Michael

Wiltshire UK

[Sathya Venkataraman]

Last night I tried drift alignment and tried for 2 hours and still was not able to get the red line straight :-(. Too much obstacle(tree etc). Will have to try again. Isn't there an easier way? 

[mj.w...@gmail.com]

Hi Sathya

Hopefully not misleading you again........

The PHD2 Drift Alignment is initially hard to understand and employ.

Which way to move the mount ? How much to move it ? How long to wait for the red line to settle ? etc

IMO it's good for occasional accurate checks on a permanent setup, but you can't afford to spend 2 hours setting up each night.

Initially I allow about 30scs of drifting after each mount adjustment, until the blue RA line seems to be stabilising along the X axis.

Read off the error of the blue Dec line, if not good enough repeat.

As the instructions say,  you only need to get to about 5arcmins or less.

Many people say that the SharpCap Pro Polar Alignment routine takes only takes a few minutes to get a good PA, and is easy to use.

Uses your guidescope and guide camera.

Michael

Wiltshire UK

[Sathya Venkataraman]

Thanks Michale. I do have Sharpcap but lately it is stuck in the first screen itself. It is detecting stars but not going to next step at all. I don't know if the LED street light infront of my house messing with that.  Will give it a try one more time 

[Ken Self]

Hi Sathya

You could try the Polar Drift Alignment tool in PHD2. Point close to the pole, make sure the mount is tracking. Select a star, start the the tool and wait till it stabilizes. Then adjust.

https://openphdguiding.org/manual/?section=Tutorials.htm#Polar_Drift_Align

https://www.youtube.com/watch?v=3tYUMmiRx2E&list=PLQvmVoMS3gIJ1AaiIzIGwbutr2z_yabD8&index=1

[Sathya Venkataraman]

Hi Ken, 

Thanks for the info, I'll try that. 

Thanks, 

VSN.

[Sathya Venkataraman]

Finally  I was able to resolve the issue and currently capturing M81. I noticed there is lot of spike in graph. Not sure what those are. Any advise? Are those ok or I should worry about? 

Here is the log https://openphdguiding.org/logs/dl/PHD2_logs_NGmC.zip

[Sathya Venkataraman]

Anyone have suggestion on these spikes? 

[mj.w...@gmail.com]

Did you pulse north until the guide star moved a lot before Calibrating ?

You haven't carried out a Guide Assistant run and accepted it's findings, including Dec Backlash Compensation ?

Also your guidescope focus is poor.

[Sathya Venkataraman]

Hi, 

When I did the calibration I simply followed the instruction "<shift>click on the 'Guide' button on the main screen and PHD2 will start a calibration run.". Is there anything more to do it?  how do I do "Guide Assistant run"? 

Thanks,

VSN.

[Sathya Venkataraman]

Found this YouTube for guide assistant. Will try tonight. https://www.youtube.com/watch?v=ff3CYMcSQhk

Thanks,

VSN