puzzling artefact in Ha

[Thalestris24]

45 minutes ago, Merlin66 said:

I'm revisiting this topic.....

I found that most (All?) CMOS sensors are fitted with microlenses and the immediate  chip cover plate can vary in thickness from 1 mm to 5 mm (!!!!)

If this was a real problem then surely it would be showing up on more and more images taken with CMOS cameras?

It seems strange the the prime example here and CN is of one star - Anitak

I've never experienced this type of issue.... we do suffer more from "ripples" in our spectrographic profiles - an intensity waviness - thought to be due to either/ both the internal structure of the silicon chip or interference between the cover plate and the silicon surface.

See: 

https://www.lensrentals.com/blog/2014/06/the-glass-in-the-path-sensor-stacks-and-adapted-lenses/

http://www.astrosurf.com/buil/CMOSvsCCD/index.html

https://britastro.org/sites/default/files/attachments/SpectralResponse_WhitePaper_April09.pdf ( thanks to Robin for the link)

 

Is there a real problem here?????

 

Isn't it more of a phenomenon rather than a problem per se? I gather it's caused by some variation of the Talbot(-Lau) effect? There is lots of physics and maths online that explains it - it's a bit beyond,me but essentially I understand it to be a diffraction effect which results in 3d self-imaging. I suppose the sensor + microlenses behave like a diffraction grating - under certain circumstances. I imagine it depends on various physical spacings, reflecting surfaces and particular light sources, angles, wavelengths etc.  (don't ask me!) which nefariously combine to generate the (unwanted) pattern. When I first saw examples it immediately reminded me of some x-ray diffraction patterns. Perhaps it actually occurs quite a lot but doesn't normally get made visible? It's quite fascinating, really. I think if  I were younger and brighter I'd probably like to delve deep into it. However, I've never (yet) witnessed it directly. Is there any connection with using an oag setup?

https://hal.archives-ouvertes.fr/hal-00998967/document

Louise

[Merlin66]

I also note the exposures were over 3 hr (!!) on a bright star............