Polar align plus GOTO

[donwaters201]

This must be a really dumb newbie question, but after I plate solve for polar alignment, how do I then get the mount GOTO in sync? Do I just do a normal two-star alignment with my mount?

[celkins]

Yes, redo your mount alignment… if you don’t, gotos will be off by the amount you moved the mount during PA

—
Carl

[admin]

Hi,

yes, although if you have got your polar alignment spot on and have also eliminated any cone error then even a 1 star align should be remarkably accurate

cheers,

Robin

[donwaters201]

I have improved on polar alignment techniques and have a rating of very/exc.
I use a Celestron CGEM mount with the required CPWI (Celestron software w/included drivers.)
After polar alignment, I manually (not slew) the OTA back to the HOME position.
Using CPWI, I use "Easy Align" which I understand uses the alignment I just did with SharpCap.

I go to PhD2 guiding and run Guiding Assistant. it tells me I am over 10 arc-mins out of polar alignment. (I have noticed that as I run this, the variation gets less.)

What is going on?

Thanks,
Don

[admin]

Hi Don,

there are a few possibilities here...

1) The initial SharpCap polar alignment is out - this is most often caused by flex between the mount and guide scope/camera as the mount is rotated in RA - see the troubleshooting guide for more info on this and how to test : https://docs.sharpcap.co.uk/4.1/#Troubl ... 0Alignment

2) The polar alignment is slipping somehow after being set. You can check by going back to polar alignment in SharpCap, letting it plate solve one frame so that the north celestial pole is shown, then rotate the mount in RA and check that the star trail circles are centered on the NCP point in the image.

3) Something is shifting as you point to different parts of the sky - this can be due to a mount sitting on a tripod on relatively soft ground - as you point to different parts of the sky, the weight distribution and forces acting on the mount/tripod change, possibly causing it to shift slightly.

cheers,

Robin

[donwaters201]

The mount is on a wheely bar without screw supports extended. Likely a source of problem.
I'll look at ways to firm it up, but I may have to accept some error, as its too convenient to do without in my situation.

Always learning.

Don

[Jean-Francois]

Hello,

In addition, if you use a Newton with a "floating" mirror ... the mirror could move in the holder and so changing the pointing.
Similar to the "plop" of the Schmidt-Cassegrain telescope by changing the focus direction.

Jean-Francois