Parallel Bands when Shooting the Sun

[Rob P]

Hi,

I'm using a (newish - 2.5 months old) ZWO ASI120 (mono) with a Lunt DS 60 B1200.

When I've used it to shoot the sun I appear to get parallel bands across the face of the sun running from bottom left to top right. I've attached two examples both of which were stacked in registax 6: Sun_142751 (stacked only; no processing) and Sun_142751w (stacked and applied wavelets coarsely to highlight the bands).

I've been using the minimum settings on the camera for exposure and gain; with the Gamma in the off position.

I'm not seeing this effect when shooting the moon or the planets.

Does anyone have any idea what may be causing this? (and I haven't ruled out operator error yet!!!)

Cheers,

Rob

[JB80]

Hi Rob,

Looks like you are getting Newtons Rings in your images. https://en.wikipedia.org/wiki/Newton%27s_rings

This is quite common though when shooting in H-alpha and is caused by reflections from the little glass window covering the sensor of the camera.

There are a few things you can try to sort this out.

1. Try tilting the camera somehow. There are actually tilt adapters you can buy for just this purpose but you may get away with a slight bit of tilt in the eyepiece holder if you can.

2. Try taking flats by defocusing on the disc of the sun and taking a short avi of that, around 300-500 frames. You then create a master flat and add it to the stack.

3. Use a bit of drift or dithering.
Let the sun move around slightly on screen, it doesn't have to be much but I find I really only get newton rings when I have perfect alignment.
Generally I just guesstimate alignment by roughly plonking the tripod in the right area, it is good enough to tack the sun for an avi but still has enough movement to knock the NR's on the head.

[Merlin66]

Rob,
As Jarrod says -it's Newton Rings....
possible aggravated by a little over processing...

[Rob P]

Ken & Jarrod,

Thanks for the information. Who'd have thought a good alignment would be the cause.

I'll have a play around and see what happens.

Cheers,

Rob

[julianh72]

There's a post on the ZWO User's Group Forum on how to address the Newton's Ring issue:

http://zwoug.org/viewtopic.php?f=21&t=1408

If fixing the alignment is troublesome, there's a suggestion to take a flat frame and remove it in software:
http://www.schursastrophotography.com/solar/Articles/solararticle5.html

[OzStarGazer]

Can it also happen without Ha?
I have a normal Baader filter and I noticed a similar phenomenon in an old photo I have (by enhancing it it is even more prominent). The second image is enhanced on purpose to show what I mean.
However it doesn't always happen. Actually this is the only photo where I can see these lines.
Or are these other artifacts?

[Merlin66]

The monochromatic narrowband certainly accentuates the Newton Rings much more than broadband light.
Your images I don't think show NR but acquisition/ processing artifacts.

[OzStarGazer]

Maybe it was this: http://www.graphics.com/article-old/eliminating-image-banding-photoshop