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Digital Weirdness

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#1 BYoesle

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Posted 23 February 2021 - 03:39 AM

While this post has an image of the Sun, I'm needing some input from general digital CMOS experts. I recently acquired a FLIR GS3-U3-123S6M 12 MP CMOS monochrome video camera to do full disc imaging of the Sun.

 

When used at an FL of 900 mm prime focus, the image is essentially perfect:

 

124546_16-01-2021_l6_ap685 - ImPPG.jpg

 

Coronado SM90/90 > ED100/900 > BF30 > FLIR Grasshopper3, captured with FireCapture, pre-processed in ImPPG, aligned and stacked in AS!3. No additional processing. Click for larger.

 

However, merely adding a CEMAX 2X Barlow delivered a strange pattern of vertical banding (which I don't think are Newton rings - but I could be wrong) and a irregular patch of fixed pattern noise:

 

Banding w FPN sm.jpg

Click for larger.

 

I'd appreciate any input about what might be causing these artifacts and how they could be eliminated or mitigated. 

 

Thanks for your time and interest.

 

 



#2 Tapio

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Posted 23 February 2021 - 03:45 AM

Those are indeed Newton rings.

See here image (and cure for it too):
https://stargazerslo...-zwo-t2-tilter/

 

The second is stacking artifact, but I don't remember cure for that.



#3 TOMDEY

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Posted 23 February 2021 - 05:24 AM

Yeah, they are unintended ghosting interference fringes exacerbated by the significant longitudinal spatial coherence of the fractional angstrom bandwidth of the etalon. A different Barlow that is specifically V-coated for H-alpha should fix the problem. Probably start by trying different make and model Barlows and/or cheating the spacings to somewhat different amplifications.

 

Similarities: Lunt makes H-alpha coating optimized Eyepieces. Ideal for your application would be an H-alpha coating optimized Barlow; I'm not sure such exist unless you do the build yourself of commission it. Zygo makes HeNe ARC coated interferometer objectives; I designed and had built custom aerospace Fizeau Interferometer Objectives... and had the shop ARC V-coat for HeNe. As intended, no annoying fringing. The Kodak coating engineer was dragging his feet on the job, so I sent the lenses to my friends at B&L and they did a fine job coating them. Be sure to request the "V-Coat for H-Alpha"; the theoretical achievable ACR is --- identically Zero with 0.05% routinely achieved.   Tom

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  • 92 Lunt H-alpha optimized coating Eyepieces.jpg


#4 SandyHouTex

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Posted 23 February 2021 - 10:11 AM

^^^^^ What he said. ^^^^^^



#5 BYoesle

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Posted 23 February 2021 - 05:32 PM

Thanks everyone. Like the Lunt eyepieces, the Coronado CEMAX eyepieces and the CEMAX 2X Barlow are actually supposed to have coatings designed specifically for H alpha. But I will try changing the spacings and using different Barlows to cover all the bases.

 

Looks like a filter-tilter is in my future ;-)

 

waytogo.gif



#6 chanrobi

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Posted 23 February 2021 - 10:02 PM

Yeah, they are unintended ghosting interference fringes exacerbated by the significant longitudinal spatial coherence of the fractional angstrom bandwidth of the etalon. A different Barlow that is specifically V-coated for H-alpha should fix the problem. Probably start by trying different make and model Barlows and/or cheating the spacings to somewhat different amplifications.

 

Similarities: Lunt makes H-alpha coating optimized Eyepieces. Ideal for your application would be an H-alpha coating optimized Barlow; I'm not sure such exist unless you do the build yourself of commission it. Zygo makes HeNe ARC coated interferometer objectives; I designed and had built custom aerospace Fizeau Interferometer Objectives... and had the shop ARC V-coat for HeNe. As intended, no annoying fringing. The Kodak coating engineer was dragging his feet on the job, so I sent the lenses to my friends at B&L and they did a fine job coating them. Be sure to request the "V-Coat for H-Alpha"; the theoretical achievable ACR is --- identically Zero with 0.05% routinely achieved.   Tom

Dang, I was just about to say this




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