19 replies to this topic

[ShiftSix]

Evening fellas, 

So I setup tonight like I always do, got 102 frames into a target everything working perfectly.   Stopped the live stack to switch targets and every time I tried to pick a new guide star/ start the guide calibration process I run into this error... 

 

"Current Dec is too high"  

 

I've never seen this before, any idea what would cause it or how to fix the issue? 

Thanks! 

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[scanner97]

It means what it says.  You're trying to calibrate using a star that's more than 30 degrees from the CE.  This just means your calibration may not be as accurate as it would be if you were closer to the CE.  You can pick a new calibration star or ignore the recommendation.

[ShiftSix]

It means what it says.  You're trying to calibrate using a star that's more than 30 degrees from the CE.  This just means your calibration may not be as accurate as it would be if you were closer to the CE.  You can pick a new calibration star or ignore the recommendation.

I guess I'm scratching my head because I picked 3 different calibration stars but kept getting the same error.

Changed targets tried again, and same error.   

[ShiftSix]

Might have solved it? maybe? 

So the dew heater's cord unplugged and I had dew forming on the lens of the guide scope.  Noticed it after I brought the setup back inside.  Maybe it couldnt get a good read on a star or something?  Not sure.

Took it back outside now and its back guiding fine.  

Not sure if it was the cause and the fix or if it was a fluke and its just working now randomly

Edited by ShiftSix, 07 November 2024 - 10:38 PM.

[jonnybravo0311]

The error means where you're pointing in the sky is too far away from the celestial equator, so calibration might not be very good. Pick a target close to the celestial equator and near to the meridian. Slew there. Then do your calibration. Once done, you don't need to do it again when you slew to a new target, unless you've rotated your guide camera (which given the equipment list in your signature, I doubt you do). Now, if for some reason you can't point to the equator (buildings in the way, trees, whatever), get as close as you can. Anywhere between the equator and 30 degrees north of it will make the ASIAir happy.

 

So, to summarize...

 

When you first setup and get yourself polar aligned, slew your scope to somewhere near the celestial equator and the meridian. Run the guide calibration. Slew to whatever target you intend to shoot and start imaging.

 

Now, if the ASIAir insists on running a new calibration every time you switch targets, you can get around that, too. Go to the guiding tab and scroll down to "Auto restore calibration". Toggle that on. It'll keep using the calibration you did near the celestial equator for your future targets.

[rgsalinger]

The OP may not actually understand declination and right ascension. I suggest buying a copy of the Deep Sky Imaging Primer as an excellent investment for anyone, even an ASIAIR user. 

[Ljubo]

If you're on target, you simply press "ignore" button. But if your target is away from the actual  point, and far towards the celestial equator, then you have to move the scope further away from the North celestial pole, and closer to the celestial equator.

[ShiftSix]

The OP may not actually understand declination and right ascension. I suggest buying a copy of the Deep Sky Imaging Primer as an excellent investment for anyone, even an ASIAIR user.

I probably could, but from my vague understanding the area I was trying to image should have been in the clear. I’ve not had issues with that area of sky prior, so I’m confused as why I would get that error now.

[jonnybravo0311]

What was the target you were trying to shoot that was giving you the "you're too far" warning?

[ShiftSix]

What was the target you were trying to shoot that was giving you the "you're too far" warning?

 

M33 at about 9pm from Wisconsin.  

[jonnybravo0311]

Yep, that's too far away from the equator.

 

M33:

 

Right ascension: 01 h 33 m Declination: +30°39'

 

That's more than 30 degrees north of the equator, which is why the ASIAir gives you the warning.

[ShiftSix]

Yep, that's too far away from the equator.

 

M33:

 

Right ascension: 01 h 33 m Declination: +30°39'

 

That's more than 30 degrees north of the equator, which is why the ASIAir gives you the warning.

So why would the Air not give me an error for imaging Andromeda?  Andromeda is +41 I guess thats whats throwing me off but I'm very new to this

[jonnybravo0311]

You slewed to Andromeda and it did a calibration at that target without giving any kind of warning? It certainly _should_ have given you the same warning, because last I checked 41 > 30 .

[ShiftSix]

You slewed to Andromeda and it did a calibration at that target without giving any kind of warning? It certainly _should_ have given you the same warning, because last I checked 41 > 30 .

  Thats what I'm saying

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[jonnybravo0311]

No clue. Either you already have a valid calibration, you missed the warning and just tapped through it, there was a software update that changed the behavior to actually warn you when trying to calibrate at > 30 degrees from the equator... or it's just a bug. Next time you've got clear skies and setup, don't do any calibration. Slew to Andromeda and calibrate. Hopefully it'll give you the warning. Cancel the calibration, then slew to M33. See what happens. If it happily calibrates without warning on either of those targets, perhaps see if you can contact ZWO and raise the bug with them.

 

Nice capture of Andromeda

[ShiftSix]

No clue. Either you already have a valid calibration, you missed the warning and just tapped through it, there was a software update that changed the behavior to actually warn you when trying to calibrate at > 30 degrees from the equator... or it's just a bug. Next time you've got clear skies and setup, don't do any calibration. Slew to Andromeda and calibrate. Hopefully it'll give you the warning. Cancel the calibration, then slew to M33. See what happens. If it happily calibrates without warning on either of those targets, perhaps see if you can contact ZWO and raise the bug with them.

 

Nice capture of Andromeda

Ha I gotcha, many thanks for your help with it.  

Maybe you can help me learn a bit about this though.  If I'm polar aligned and on an equatorial mount, why would alignment/ calibration/ or guiding be affected if I'm looking at a target north of 30 deg?  shouldn't they all be rotating on the same axis that my polar alignment is on? 

I feel like im missing something vital here to the understanding of this lol

[scanner97]

Calibration involves measurement of movements by the mount.  All measurements involve errors.  The largest movement in RA will occur when you're at Dec=0.  Small errors in measurement will have less of an effect when the movement being measured is larger.  Thus, measuring close to Dec=0 will give you the best chance of a more robust calibration.  Calibrating farther away won't necessarily cause a problem - it just has a higher probability of being slightly less accurate.

 

The reason you want to be close to the Meridian is to reduce the impact of seeing, which again translates to improved accuracy.  So the "best" place to calibrate is at the intersection of CE and M on your sky.  If you have obstructions, so that position isn't readily visible most of the time, you do the best you can.  Higher in the sky is generally better, and closer to the CE.  If you can't have both, I don't have an algorithm for the trade-off.    But, as you saw, you got a very nice image with a less than "ideal" calibration.

 

On the failure of Air to report an error at M31, couple of other possibilities...

• The pointing position in the Air is off a bit for some reason.  (Seems unlikely if it found M31 just fine!)
• The calibration star selection algorithm in the Air version of phd2 has some quirks.    (I don't own one so I can't comment.)

I gather the version of phd2 used in the Air was "customized" and is a bit of a black box.

Does the Air version include the Calibration Assistant?  I'm guessing not as that requires some user input, but it's an easy way to choose a calibration location nearer to CE/Meridian.

 

Good luck!

Edited by scanner97, 08 November 2024 - 11:25 AM.

[ShiftSix]

Calibration involves measurement of movements by the mount.  All measurements involve errors.  The largest movement in RA will occur when you're at Dec=0.  Small errors in measurement will have less of an effect when the movement being measured is larger.  Thus, measuring close to Dec=0 will give you the best chance of a more robust calibration.  Calibrating farther away won't necessarily cause a problem - it just has a higher probability of being slightly less accurate.

 

The reason you want to be close to the Meridian is to reduce the impact of seeing, which again translates to improved accuracy.  So the "best" place to calibrate is at the intersection of CE and M on your sky.  If you have obstructions, so that position isn't readily visible most of the time, you do the best you can.  Higher in the sky is generally better, and closer to the CE.  If you can't have both, I don't have an algorithm for the trade-off.    But, as you saw, you got a very nice image with a less than "ideal" calibration.

 

On the failure of Air to report an error at M31, couple of other possibilities...

• The pointing position in the Air is off a bit for some reason.  (Seems unlikely if it found M31 just fine!)
• The calibration star selection algorithm in the Air version of phd2 has some quirks.    (I don't own one so I can't comment.)

I gather the version of phd2 used in the Air was "customized" and is a bit of a black box.

Does the Air version include the Calibration Assistant?  I'm guessing not as that requires some user input, but it's an easy way to choose a calibration location nearer to CE/Meridian.

 

Good luck!

This makes a ton of sense.  

I never considered the speed of the rotation increasing decreasing as you get closer to the pole. 

Thanks! 

Edited by ShiftSix, 08 November 2024 - 01:49 PM.

[jonnybravo0311]

This makes a ton of sense.  

I never considered the speed of the rotation increasing as you get closer to the pole. 

Thanks! 

It would be exactly the opposite. The earth rotates once in 24 hours. Let's assume you're standing 50 feet from the pole. You only have to travel a distance of about 314 feet in that 24 hours (circumference is 2 * pi * r). Someone standing at the equator has to travel about 25000 miles in that same time. Same thing holds true in the celestial sphere

[ShiftSix]

It would be exactly the opposite. The earth rotates once in 24 hours. Let's assume you're standing 50 feet from the pole. You only have to travel a distance of about 314 feet in that 24 hours (circumference is 2 * pi * r). Someone standing at the equator has to travel about 25000 miles in that same time. Same thing holds true in the celestial sphere

  Doh,  That's what I meant lol 

Replying between meetings. haha