Calculating Field Rotation With an Alt Az Mount For Solar Timelapses

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marktownley
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Calculating Field Rotation With an Alt Az Mount For Solar Timelapses

Post by marktownley » Tue Apr 16, 2019 8:32 am

As we all know observing using an alt az mount causes field rotation. This would be a pain for solar if you were timelapsing a sequence of images as the final animation would appear to rotate around the centre of the frame.

I'm wondering is there an easy way to calculate this?

By that I mean could, for example, if had took a sequence of images with a particular cadence calculate how much field rotation in degrees has happened between each sub frame in the sequence. That way when I created the final animation it would be very easy to write an action in Photoshop that rotated each image automatically by a certain amount. Thus, derotating the final sequence.

I have looked online but is all full of lots from the world of nighttime astronomy. Any ideas anyone?

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Re: Calculating Field Rotation With an Alt Az Mount For Solar Timelapses

Post by PDB » Tue Apr 16, 2019 9:56 am

Mark, have you tried this in AS!3? Might solve your problem. No idea if it works. (but seems you need to calculate de rotatiion degree first, think I have this somewhere but need to dig very deep ....)

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Re: Calculating Field Rotation With an Alt Az Mount For Solar Timelapses

Post by krakatoa1883 » Tue Apr 16, 2019 10:43 am

Hi Mark, for a given day and time Helio Viewer software calculates the parallacting angle of the Sun as seen through an alt-azimuth telescope (http://www.petermeadows.com/html/parallactic.html)
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Re: Calculating Field Rotation With an Alt Az Mount For Solar Timelapses

Post by marktownley » Tue Apr 16, 2019 5:20 pm

Thanks guys. I guess with AS3 you could plug in each of the stacked frames as a sequence that would make up the animation and then see if it would derotate. Helioviewer would allow to work out the parallactic angle at the start and end of the animation sequence and then the rotation per frame could easily be calculated and applied in PS.

OK, just need to get a good enough and long enough run of data to test it with :lol:
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