Aligning on Refracted NCP

Using SharpCap's Polar Alignment feature
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amorrison
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Aligning on Refracted NCP

Post by amorrison » Sun Jul 12, 2020 3:11 pm

Currently I use the big "adjustment numbers" on the screen to get to the True NCP then zoom in on the image and move the red rotation axis "X" over the Refracted NCP. Is there a way to get the adjustment numbers to reference the refracted pole instead of the True NCP?

Thanks.

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admin
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Re: Aligning on Refracted NCP

Post by admin » Sun Jul 12, 2020 8:09 pm

Hi,

I always have to think about this about three times when we discuss anything related to the true and refracted positions of the pole. As far as I'm aware SharpCap should be guiding you in on the correct version if you have turned the refraction correction on – refraction tends to make things appear higher above the horizon than they really are, so you should end up aligning on the one that is slightly closer to the horizon of the two which will be the position of the true NCP rather than the refracted NCP.

Cheers, Robin

amorrison
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Joined: Wed May 15, 2019 10:11 pm

Re: Aligning on Refracted NCP

Post by amorrison » Mon Jul 13, 2020 10:10 pm

Thanks for the reply Robin.

TheSkyX software recommends aligning to the refracted pole. I have the refracted option checked in Sharpcap Pro and the big numbers take me to the true NCP. I can see the big X on top of the True NCP in the image. The refracted pole is shown slightly above it. So I then move the axis up till the red X is on the refracted pole. At first, I aligned to the big numbers thinking that was the refracted pole since I had the option checked, my t-point run told me to raise the axis about the amount I would have needed to reach the refracted pole in the image.

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Re: Aligning on Refracted NCP

Post by admin » Tue Jul 14, 2020 6:34 pm

Hi,

just to check that we are using the same terminology – in the SharpCap polar alignment routine, the true pole is the point you need to aim at to make your mount axis parallel to the Earth's axis of rotation. The refracted pole is the point in the sky where a star that was at declination exactly 90° would appear.

If you want to align with the refracted pole for some reason, the easiest thing to do is just to turn off the refraction correction option – then SharpCap stops making the distinction between the two and uses the refracted pole for all calculations.

Cheers, Robin

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