Newton Rings and CCD Fringing

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Merlin66
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Newton Rings and CCD Fringing

Post by Merlin66 » Thu May 17, 2018 1:57 am

I'd like to investigate further the incidence of NR and CCD fringing.

This only occurs when very narrow band filters are used in monochromatic light. So, these usually appear in solar Ha imaging.

The NR are caused by interference between the cover plate and the underlying CCD/ CMOS chip. The extent and contrast of the NR can vary camera to camera and are more obvious when larger f ratios are used.
The accepted solution is to either slightly tilt the chip, thereby changing the effective spacing of the cover plate/ chip or by inserting a weak (2 to 4 degree) prism immediately in front of the chip.

CCD fringing, seen in many solar images as a continuous series of well defined lines across the image (much tighter and consistent than the normal NR) are caused by interference within the chip structure.
(See: https://books.google.com.au/books?id=rk ... ng&f=false)

I think it would be useful, and constructive, to record the performance of the cameras we use in terms of NR and Fringing generation.
The data required is straight forward: the camera details, the f ratio used and an example showing the NR/ Fringing.

The DMK 41 and DMK 51 don't seem to have any issues... the ASI 174mm generally shows NR and the ASI 183mm no NR.

What's your experience?????
Either post results here or drop me an email kenm(dot)harrison(at)gmail(dot)com
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marktownley
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Re: Newton Rings and CCD Fringing

Post by marktownley » Thu May 17, 2018 5:10 am

Hi Ken.

My PGR Blackfly IMX249 camera shows newtons rings in Ha light regardless of focal ratio, however none at all in CaK.

The PGR Chameleon 3 shows rings in Ha regardless of focal length, however in CaK the issue is dependent on the barlow lens used - some combinations it exists, some it does not.

Sorry don't have images to hand.

Mark
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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GreatAttractor
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Re: Newton Rings and CCD Fringing

Post by GreatAttractor » Thu May 17, 2018 11:48 am

Mark, could you specify you Chameleon3's model number? My CM3-U3-13S2M-CS (sensor: ICX445) doesn't show rings in any of my Hα setups (Omega Optical, Lunt 35, Lunt 50 and their mods, Barlowed or not).
My software:
Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
My images

SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)

bart1805
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Re: Newton Rings and CCD Fringing

Post by bart1805 » Thu May 17, 2018 5:32 pm

Dmk41 mono and PGR Grasshopper IMX174 mono. No Newton rings when used in primary focus. But with 2,5x Powermate both camera's show them really, really well....

Solution: 2 degrees wedge prism. And presto: no Newton rings at all.

Macavity
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Re: Newton Rings and CCD Fringing

Post by Macavity » Sat May 19, 2018 6:25 am

Like many Solarites, I started with a Lunt50/B600 (f/7.5) + ZWO ASI120MM!
The latter a "Fine Thing" but (as often noted) producer of Newton's Rings?
Below a slightly "unsharp-masked" single frame from then typical video! :P

sharp000.jpeg
sharp000.jpeg (480.67 KiB) Viewed 540 times

A 2x Barlowed (f/15) image with Lunt50 / ASI120MM gave similar intensity 
rings albeit with wider(?) spacing. ALL characteristic of Aptina CMOS chips?
I tried Flats (cling-film and de-focussed) and "tilting", but wasn't too keen!
I was able to produce (to me) satisfactory images using the DRIFT method.

But I got a bit fed up with having to remember to drift... re-center... etc. :roll:
So I then opted for a "slow but steady" (frankly NOT inexpensive!) DMK41.
This banished the NRs, but had bigger (4.4/3.75 mu) pixels and in my case
showed a region of "variable" pixels. I now *needed* FLATS for everything!

Then my EPIPHANY (or rather I finally heeded suggestion of certain folk?): :D
Simply I bought a (FLIR) Chameleon3 Cam. NO MORE NRs! Back to 3.75mu
pixels and (although my Notebook/Laptop is USB2.0) worked at faster rate.
(Cam works great with ED80/Lunt50 Frankenscope upto f=1200mm; f/15)

For me: the "secret" was CCD over CMOS... or a Sony ICX445 Chip anyway? :cool:
I even vaguely ponder getting a SPARE, while the "going remains good"...

For fellow UK readers, I was able to source the CM3-U3-13S2M-CS Cam via:
https://www.edmundoptics.co.uk/cameras/ ... 0-Cameras/
Arrived by return (and still yet?) ex-stock! (Have no financial interest etc.)

Regards, Macavity / Chris

P.S. I notice a fellow solar imager using a color ASI120MC without NRs?
But probably doesn't realise the ultimate resolution from his pixels...
Despite all above, I have other uses for both my ZWO120MM & MC Cams! ;)

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