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Is this "Blue APO Histogram" normal?

Meade Optics Astrophotography
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#1 Dr. Frankenkeim

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Posted 22 February 2021 - 10:27 PM

Hi Guys,

 

I just recently made the switch from a cheap telephoto lens to a Meade 6000 70mm Quad.

 

I was very excited to finally have a dedicated telescope. I use a DSLR and I am used to the green tint, but my first session with the Meade resulted in all pictures being "blue", which you can also see on the attached histogram. The histogram of my DSLR when I used the cheap telephoto lens was much more aligned.

 

Should I expect this or is there maybe an issue with the optics? Those were only 25 second exposures and the "blue dominance" increased when I increased exposure lengths. 

 

I was able to adjust for it all this in post and the session turned out ok, but now I worry about the optics.

Any thoughts?

 

Meade 6000 70mm Quad.jpg



#2 DJL

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Posted 22 February 2021 - 11:26 PM

Is this happening in the subs or only after stacking? Could be something going wrong in the stacking process, like running light pollution filter on a nebula. Maybe share the image as well?



#3 Dr. Frankenkeim

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Posted 22 February 2021 - 11:53 PM

It only in the subs (the histogram is from the raw sub).

 

After stacking and color calibration is the stack looks fine and I do not see noticeable chromatic aberration but I also only took one session so far.

Attached Thumbnails

  • Screen Shot 2021-02-22 at 8.41.10 PM.jpg


#4 sharkmelley

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Posted 23 February 2021 - 06:51 AM

It looks like the sky background is blue.  Was the moon up?

 

Mark



#5 Alex McConahay

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Posted 23 February 2021 - 09:02 AM

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



#6 Der_Pit

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Posted 23 February 2021 - 09:07 AM

My guess is either blue-dominated light pollution or a wrong/weird white balance setting....



#7 jerr

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Posted 23 February 2021 - 09:16 AM

Did you use any filter?



#8 Dr. Frankenkeim

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Posted 23 February 2021 - 03:30 PM

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?

 

Mark

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 smile.gif ).  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

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?

 

 

 

Did you use any filter?

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!

Frank



#9 Alex McConahay

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Posted 23 February 2021 - 04:21 PM

What camera are we talking about?

 

And I stand by that this has nothing to do with the optics. No matter how bad the color correction, it would not have shown like that in a histogram. 

 

 

 

Alex



#10 sharkmelley

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Posted 23 February 2021 - 04:30 PM

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 smile.gif ).  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?

Yes, just like the sun makes the sky blue then so does the moon.  But a lot dimmer of course!

 

Mark



#11 Dr. Frankenkeim

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Posted 23 February 2021 - 05:06 PM

What camera are we talking about?

 

And I stand by that this has nothing to do with the optics. No matter how bad the color correction, it would not have shown like that in a histogram. 

 

 

 

Alex

Alex - that is very good to know. The camera is an entry level Nikon D3400.

 

 

Yes, just like the sun makes the sky blue then so does the moon.  But a lot dimmer of course!

 

Mark

Mark - I guess I did not think about this way. Thank you

 

 

 

Thank you both - I am glad I posted this and I am relieved now. 

Frank




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