Hi Guys - thank you so much for you help.
I combined my answers:
It looks like the sky background is blue. Was the moon up?
Hi Mark - that would make senes. I took the test shots on February 18 between 8:30PM and 10:30PM PST (APO pick-up date ). The moon was at 44.26% that night.
When I previously imaged with the lens, and the moon being partially up, I felt as if the histogram was "only" moving proportionally to the right vs only one channel pulling out to the right. Would the moon disproportionally impact the blue channel?
That is not about the optics. Even in the worst non-achromatic scope the blue fringes or red fringes would not make that kind of difference.
What Bayer pattern did you put into the processing. It looks like RBBG instead of RGGB perhaps.
Alex - this is helpful to know. The histogram and screenshot was from the pre-processed picture. When I stack the the lights (using RGGB), and color correct them, the stacked file seems ok, but the pre-processed file does show this blue shift.
My guess is either blue-dominated light pollution or a wrong/weird white balance setting....
Light pollution is definitely a possibility. I live in LA County so there for sure is...a lot of light.
The weird thing is that I usually image to West which has the "less" light domes, as far as LA County is concerned, but my old (stock / cheap) lens did not show this blue shift (not that much at least). Maybe the APO just separates the chancels better?
Hi Jerr - no filters. The DSLR goes straight into the APO. I used the same setup and setting I did with the old stock lens.
Thank you all!