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Understanding Meridian Flip.

Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA) Acquisition Meridian Flip Deep Sky
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Mossyback avatar
Mossyback avatar
Finally getting to know N.I.N.A. but haven’t mastered the “flip”. It works as it’s supposed to but the images after the flip are reversed.

Questions: 

1. After the flip should I have N.I.N.A. do a platesolve? Will that solve the problem? Refocus?

2. Is there any process in Pixinsight that can “fix” the reversed images? I’d like to save them for processing if possible.

Hank
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Christian Bennich avatar
Christian Bennich avatar
I have never had any issues in PI with the "reversed" images as a result of a Meridian Flip. 
It's all fixed during the WBPP Script Process.

I am working with ASIAIR - I don't need to do a plate solve after a Flip - the plate-solving is done as an astrometric solution added to your images when going through the WBPP process
Pelayoaviles avatar
Pelayoaviles avatar
Reversed images are what you shall expect after a flip and they are perfectly fine. During pre processing the software will handle that and it will just rotate the images as needed so all of them match perfectly.

Anyway, you should perforn a platesolve right after a meridian flip, in my opinion.  It will not fix the reversed images 'problem' (there is nothing to fix), but you should try to get all the images dead centered in the same coordinates, reversed or not. Equatorial mount lack of absolute preccision could introduce some errors after a flip. Nothing catastrophic, probably not a big deal, but plate solve is for free and takes a few seconds. So why not doing it after a mount slew?

If you do not perform plate solving after mount slews, when aligning the images potential errors in centering could cause that the images do not overlap perfectly. Meaning, you will lose certain amount of pixels on the borders of the image.
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Scott Badger avatar
Scott Badger avatar
I'm still using the older version of NINA, so maybe the newer one is different, but note that if the target isn't listed in the sequence, after a meridian flip NINA will platesolve to the mount's position just before the MF, not necessarily to the target. Because NINA pauses guiding at the same time it pauses imaging (prior to the flip) with NB especially where the exposures are 10 minutes, the pause in guiding can be nearly that long. So, likely a fair amount of drift and the position NINA platesolves to (without a target listed) can be well off center. Learned this the hard way using some generic sequences…..

Cheers,
Scott
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Joe Linington avatar
Joe Linington avatar
If you have a target in the sequencer, it will automatically plate solve and slew to the target as part of the meridian flip. If you use the advanced sequencer you can also add the trigger to periodically plate solve and trigger an adjustment if the image gets to far out of place. After a flip, the image should be reversed, you just rotated the camera 180*. Nothing you can do about it but every stacking software I have ever used takes care of this during registration and your flats, darks, etc stayed aligned because they are aligned to the sensor not the image.
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Mossyback avatar
Mossyback avatar
Thanks folks for all your help. Tonight’s going to be clear so I can set up and stop worrying.smile
Tim Ray avatar
Tim Ray avatar
Hank.

Everyone has the images flip (rotate 180 degrees) after a meridian flip. This is not a problem. NINA or SGP or TSX understands that. So if you were imaging a 0 degrees relative then do the flip your orientation is now 180 degrees relative. You use the same flats and flat darks (Bias if CCD) for both sides of the meridian. Unless, you actually rotate the camera back to 0 degrees after the flip. Then you would need separate calibration frames for each side of the meridian. With that said, when you stack for pre-processing will autorotate the sub, after calibration, to the correct orientation of the reference sub during the integration process.

Start your run, auto focus when needed, do the meridian flip, plate solving will re-center the object, continue the sequence. Understanding the images displayed after the flip will be displayed 180 degrees rotated from before the flip…

Hope this helps.

CS - Tim
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