Newton Rings and CCD Fringing

[Merlin66]

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

[Freddie]

I get NRs on both my ASI 120 and 174 when using the Quark. A VERY slight tilt gets rid of them. They show on all 3 scopes I have used 400mm FL 5FR, 600mm FL 5FR and 988FL 6.5FR.

[Davey-T]

I get them with PGBfly camera without a .5X focal reducer but not with one so as you say longer focal length affects it.

Will try and find some examples, may have to take some as I don't usually save them.

Dave

[xtreemchaos]

i dont get them at all with all my fracs, i have adjusted the scopes so the light path is bang on, a bit of focuser slop is the usal problem, nothing a lazer and a bit of paper wont sort out. charl. 

[Pete Presland]

I don't get them other my DMK21au618 either.

[Lowjiber]

I use a tilter on one of my ASI174MM cams.  I've never experienced the "fringing", but NRs are present to a certain degree.  The tilter will take them away, but they're easily "fixed" in PS too.

Yesterday, I was using the untilted-cam (174) and had some.  I've attached it below.

I use three APO scopes with the Quark... f/5.9, f/7.5, and f/9.  The image attached was with the f/9 scope.

Interesting thread.

Clear Skies