11 replies to this topic

[Whereisclearsky]

Hi,

 

So some say that if I image something on western sky then

i should do calibration in that direction, and should be close to meridian and equator, close to Dec 0.

 

I don’t really get it, as shown on screenshots below, when look West, the equator line isn’t there onviously, and the meridian line drips quickly close to low horizon.

 

 

I was imaging Markarians chain last night from UK and was really confused where to point the scope for best calibration.

 

Also in Asiair guider settings there is a flip option, should I tap it after meridian flip?

 

Thanks

Edited by Whereisclearsky, 22 May 2025 - 01:16 PM.

[klangwolke]

I am not sure of that advice; it might be true; but what has worked for me is to calibrate near the celestial equator to get the most star movement and near the equator to minimize atmospheric distortion. I have never had to manually use the calibration flip button in guiding after an automated meridian flip. I have used it when I know I’ve calibrated before a meridian flip and started a target after the flip.

[Whereisclearsky]

I am not sure of that advice; it might be true; but what has worked for me is to calibrate near the celestial equator to get the most star movement and near the equator to minimize atmospheric distortion. I have never had to manually use the calibration flip button in guiding after an automated meridian flip. I have used it when I know I’ve calibrated before a meridian flip and started a target after the flip.

It's explained here:

https://youtu.be/HXR...re=shared&t=757

I've seen some reports that it does in fact improve guiding.

Edited by Whereisclearsky, 22 May 2025 - 06:12 PM.

[rgsalinger]

The only reason to calibrate just west of the MERIDIAN is so that you don't have to worry about the mount hitting your tracking limit and stalling or deciding (amusingly) to flip in the middle of a calibration. Other than that, it makes no difference which side of the sky you use to calibrate a guiding system.  Doing it at DEC zero is the best idea unless you plan to image very near the celestial pole - above DEC 70 or so. In that case you may want to try calibrating at your target. 

[PIEJr]

I normally build my calibration files (Or Alignment as some say) with 10 Westward, and 10 Eastward calibration stars.

(For calibration, I'm an over achiever. All it takes is a bit more time.)

Since I don't move my mount or telescope anymore, I just let it dry (if need be) and cover it with my coverings, I don't have to run a calibration (alignment) very often.

But, Rene` agreed with my excessiveness that more Stars in the Model (alignment) gives your mount more zeroing. Which was my logic to doing ten.

After 7 or 8 stars, I could not see much improvements in slewing accuracy. But I went ahead and did more.

 

But even back when with my AVX I would do extra stars.

[michael8554]

The "real" PHD2 advises to Cal near south and near Dec = 0.

 

For a target in the west then you could Cal pointing close to south, after the Flip, but not a long way west.

 

Some mounts will respond to the flip option and reverse Dec commands.

 

If Dec corrections after the flip cause the Dec error to continue to increase, then the Flip setting isn't being recognised and you will need to recalibrate after the flip.

[PhilHoyle]

I don’t really get it, as shown on screenshots below, when look West, the equator line isn’t there onviously, and the meridian line drips quickly close to low horizon.

[PhilHoyle]

The meridian is an imaginary line that goes from due south, through zenith, to due north. It never gets close to the horizon and is always perpendicular to it.

[Whereisclearsky]

The meridian is an imaginary line that goes from due south, through zenith, to due north. It never gets close to the horizon and is always perpendicular to it.

Ok I have confused meridian with celestial equator. 

[Spaceman 56]

The meridian is an imaginary line that goes from due south, through zenith, to due north. It never gets close to the horizon and is always perpendicular to it.

Good answer.  

 

The Meridian can also be thought of as a line that divides the Eastern side of the sky, from the Western part of the sky.

 

Phil might also like to answer where the Dec equals Zero line is to be found ?   

[PhilHoyle]

The Dec equal zero line is the celestial equator. That's an imaginary line directly above Earth's equator. It runs parallel to the east-west direction. When facing due south, for the northern hemisphere, it is 90 degrees minus your latitude above the horizon. It gets closer to the horizon as you go east or west.

[Spaceman 56]

The Dec equal zero line is the celestial equator. That's an imaginary line directly above Earth's equator. It runs parallel to the east-west direction. When facing due south, for the northern hemisphere, it is 90 degrees minus your latitude above the horizon. It gets closer to the horizon as you go east or west.

Thanks.  

 

For my location (35 degrees South) in the Southern Hemisphere, I therefore have to point my telescope towards the north, roughly at an angle of 55 degrees so that I can point towards the celestial equator.

 

Where is Clear Skies would apply the same theories to his specific location, and calibration should work better, once applied near this position.