M81 & M82 - Dual colored stars

[gferla]

Hello everyone,

I was wondering what may lead to dual-colored stars?  There are a number of stars that are half blue and half orange in this image.  This image is processed from a Nikon D7500 OSC, unmodified in PI using the following steps - DynamicCrop, channel separation, LinearFit, ChannelCombination, Deconvolution with PSF, DBE, BN, CC, L-extraction, LRGB combination, nonlinear stretch, HDRMultiScaleTransformation, SCNR, ACDNR, then a bit of curve and histogram tweaks.

Full mage is here - https://astrob.in/382968/0/

Thanks!

Guillermo

[Geoff]

Was the object low in the sky? If so, it could be atmospheric refraction.

[gferla]

I'm normally trying to shoot as close to zenith as possible, which would put that target at about 70 degrees, so not sure if that's the issue.  There are definitely seeing issues, as I'm in the mountains, but I'm not sure if that would cause that effect.

Thanks for responding!

[chris.bailey]

Was it really cold? Star shapes are odd. Some of the early ZS61's had issues with pinched optics at low temperatures. The colour fringing looks optical to me.

[gferla]

Chris,

Yes, it was cold - probably around 5 - 10 F.  The Z61 was purchased just this past September, so I'm not sure if that would qualify as an early model.  I sent William Optics an email asking about the diffraction patterns on the stars thinking it could be an issue with pinched optics, and they replied that it was normal and due to the collimation screws on the lens cell.  Is it possible that the screws could cause a change in color?  Seems questionable to me.

Thanks!

[rdryfoos]

It may have something to do with how the subs were registered and integrated.  Also, if conditions fluctuated wildly, the various filters could have yielded a wide range of FWHM values which when stacked could produce strange color effects.  Not only is there a star color issue, but a star morphology issue as well--which I think is due to conditions (hopefully not  something in the sco[pe
Rodd

[dld]

Since you are imaging with a stock DSLR, I would first suggest attempting a more simpler workflow, i.e., no deconvolution and LRGB treatment. Your workflow involves many steps where things can go wrong.

And out of curiosity, how the single raw lights look like? Does this problem appears at the single out-of-camera raw light frames?