Newton's rings (?) - Help please.................

this is the main message area for anything solar :)
Post Reply
User avatar
Gordon Ewen
Almost There...
Almost There...
Posts: 539
Joined: Sun Apr 20, 2014 10:15 am
Location: Moggerhanger, UK
Been thanked: 257 times
Contact:

Newton's rings (?) - Help please.................

Post by Gordon Ewen »

I have a ZWO ASI120MM-S USB3 camera I have been using for a few weeks. At f6 on the Lunt 152 and any focal length for white light imaging it is great. However, when I try to Barlow the Lunt I get what I assume are Newton's rings. Why am I only assuming? Because the tried and tested methods of removing them don't seem to work. I have used flat fields (generated by the 'poly bag' or defocus method) in both Autostakkert and AviStack and the rings are not removed, in fact they seem to get slightly worse. I have also tried the tilt adjuster from Teleskop-Service and so far I can't make any impact on the rings. As you can imaging I am getting rather frustrated as it is at higher focal lengths the Lunt comes into its own. Does anyone have any thoughts or advice on how I can get rid of the rings? I have attached a cropped photo. I would be eternally grateful if someone has the answer!
Regards to all
Gordon
Attachments
Newton's rings 1.jpg


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
User avatar
grimble_cornet
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3537
Joined: Tue Jul 10, 2012 5:10 pm
Location: UK West Midlands
Been thanked: 47 times

Re: Newton's rings (?) - Help please.................

Post by grimble_cornet »

Hi Gordon. Its not very obvious from your image that you are suffering from Newton's rings (you should see some of my images taken in Ha with the ZWOASI120MM) - but I can spot them from bitter experience :evil:

Using my SM40 and DMK41 combination I only ever get NRs in Ha when using a x2 Barlow or - far worse for some reason - a x2.5 Powermate. With The ZWOASI120MM I get mild NRs at native fl and horrendous ones when I add a Barlow or Powermate. It even produces NRs in CaK with a x2 Barlow.

I have tried cling-film flats which work with my DMK41 and in good seeing they just about make the image usable but in poor seeing.....YUK!
I bought the same tilt adapter that you have (having made a crude version out of plywood a couple of years ago) and was really disappointed that it had very little effect with the ZWO. The adapter plus cling-film flat produce OK results in good conditions but not such that I would want to use the ZWO as my main camera for Ha. Pity because it is a superb camera for white light solar, lunar and planetary use.

My solution was to get a PGR Grasshopper which, so far shows no NRs :P

However, I might have another suggestion which could be worth exploring if you want to stick with the ZWO....

I came across a blog by a guy called David Cortner: http://www.davidcortner.com/slowblog/20130513s.php
He describes his experience with the tilt adapter and ZWOASI120MM and concludes that the tilt is not great enough to solve the problem. He explains how he modified it by adding longer screws to produce excellent results. I made the modification last week but have been obsessed with my new camera during the very few spells of sunshine :oops:
David also suggests that another approach worth trying is to apply a Fourier transform to the image. My maths is a bit rusty but I remember enough to know that it is a very complex, time consuming process but, of course, computing power can solve most problems! A free software tool is available as a PS plugin from a firm called 4N6:
https://dl.dropboxusercontent.com/u/679 ... /howto.htm
It is a 32 bit plugin and will not work in 64 bit versions of PS (under Windows anyway) but, if you have a 64 bit version of PS you probably have the 32 bit version installed as well as it does so by default.
The instructions on the 4N6 site are not exactly easy to follow (to my poor old brain anyway) but basically, once you have installed the plugin.......
Open your image
Click on Filters, select Forensic filters (bottom of the list) and FFT (the upper one of two).
A complex 4-part pattern will appear.
Open the channels tool and select just the red channel. You will see the pattern is now grey with a bright hazy centre.
If you have obvious NRs in your image, you will probably see small bright points either side of the bright hazy part. In the image below they are at 1 and 7 o clock positions and quite bright as the NRs are pretty strong. In images with more subtle NRs the spots are smaller and less obvious.
NR Pattern.jpg
NR Pattern.jpg (181.5 KiB) Viewed 2777 times
Now select the Spot Healing Brush tool, set the diameter to that of the bright spots and click once over each one to remove them.
Now select RGB - all channels, go back to the filters menu and select Forensic, Reverse FFT (the second one).
I have found that this works very well with most images but I seem to remember that they have to be in 8 bit RGB format for the filters to work - check the bumph on the 4N6 website under pattern removal help for their plugin.
I just tried it on a coloured, inverse disc image I took recently - far from the ideal as you would want to run this process before inverting, colouring and final tweaking , hence the colour change and slight limb erosion - but it might give you some idea of the power of the technique?
Inverse Disc SM40 ZWO ASI120MM 2014 0308 0818 ut.jpg
Inverse Disc SM40 ZWO ASI120MM 2014 0308 0818 deringed ut.jpg
Hope this has been of some interest.

Mike


.

.



.


Mike Garbett

Selection of Solar and Deep Sky images on Flickr: https://www.flickr.com/photos/mikegarbett/
User avatar
sullij1
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2249
Joined: Wed Mar 28, 2012 4:29 am
Been thanked: 1 time

Re: Newton's rings (?) - Help please.................

Post by sullij1 »

Sometime I do not have to correct the image even though NR in the raw image are obvious, just stacking alone will remove them. Did you try to stack without any correction method i.e. use no flat at all? Try that first and see how it works.

Let me know how it goes.

NR in HiRes images with CMOS are pretty common and the reason most folks are sticking with the CCD. CCD are causing less problems in HiRes.


Look Up!
User avatar
pedro
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 12256
Joined: Sun May 01, 2016 8:26 pm
Location: Portugal
Has thanked: 14 times
Been thanked: 6577 times
Contact:

Re: Newton's rings (?) - Help please.................

Post by pedro »

I agree, Newton rings are common in CMOS cameras. I had lots of NRs with a QHY5 that I used to image the sun a few years ago. When I bought a DMK everything changed.


User avatar
grimble_cornet
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3537
Joined: Tue Jul 10, 2012 5:10 pm
Location: UK West Midlands
Been thanked: 47 times

Re: Newton's rings (?) - Help please.................

Post by grimble_cornet »

Agreed John. My DMK21 and 41 both produce mild ones when used with a Barlow but they can get pretty bad in really poor seeing.


.

.



.


Mike Garbett

Selection of Solar and Deep Sky images on Flickr: https://www.flickr.com/photos/mikegarbett/
User avatar
Davidm
Almost There...
Almost There...
Posts: 824
Joined: Mon Jul 28, 2014 6:53 am
Has thanked: 1 time
Been thanked: 289 times

Re: Newton's rings (?) - Help please.................

Post by Davidm »

If you use a flat to try to remove the rings, make sure that you take the flat .avi as close in time to your main .avi. In my early attempts to use flats, I took the flat after a bunch of different images, and found that a small change in brightness in the overall image as the sun gained altitude actually increased the rings in my image. This effect was worse where I used to live in the Middle East, where dust haze meant the sun brightened considerably as it rose, but may be a factor where you are as well. When I took my flat close to the time of the main image, I was pretty much able to remove all the rings using a standard defocused flat.

PS, I am sure you do this already, but of course you need to ensure your capture settings for the flat are identical to the main capture.


Lunt LS152T (DSII and CaK module), Coronado Helios 1, Grasshopper 3 2/3" CCD
User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17948
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Been thanked: 1 time
Contact:

Re: Newton's rings (?) - Help please.................

Post by swisswalter »

Hi Gordon

I cant see your NR on my monitor, how ever I can see Mike's. Apart of tilting the ASI even more, I can't see any other easy help.


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
User avatar
Gordon Ewen
Almost There...
Almost There...
Posts: 539
Joined: Sun Apr 20, 2014 10:15 am
Location: Moggerhanger, UK
Been thanked: 257 times
Contact:

Re: Newton's rings (?) - Help please.................

Post by Gordon Ewen »

Mike, Sullij, Pedro, John, David and Walter, thanks for your replies to my question, good to hear about your experiences. I hadn't heard that CMOS sensors are regarded as more prone to Newton's rings than CCD's. I am considering getting a camera with a slightly bigger chip so that's given me food for thought.
Mike, I had come across David Cortner's article on getting rid of the rings and that was why I bought the TS tilt adapter. I also bought some longer grub screws too, but so far no luck using it. I will check the tilt angle and may have to get some longer grub screws and lock screws. I haven't tried the Photoshop plug in yet, I had hoped the tilt adapter would solve the problem; if I can't get rid of them I will try the plug in.
Sullij (have I got your name right?), I have tried without using a flat and the rings are still visible. Strangely, one time the flat method in Autostakkert worked but not since.
John, interesting point abut DMK's. I used to have the 618 chipped camera and have used 31AU and 41AU cameras in the past and never saw Newton's rings. I prefer the image quality with the ZWO but the rings are a nuisance.
David M, you have me thinking now. As I mentioned above, I once got a good result with making a flat in Autostakkert and that would have been using the defocus method. Since then I have been using the poly bag method but this dimmed the image so much I had been adjusting the exposure and/or gain. I will have to go back and have another go at the defocus method and not adjust the exposure and gain. Interesting thought.............
Walter, could it be a screen calibration issue.................................. sorry if that is a bit cheeky! I can see them ok when viewing from this site.
Thanks again for all your input, appreciate it.
REgards
Gordon


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
User avatar
sullij1
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2249
Joined: Wed Mar 28, 2012 4:29 am
Been thanked: 1 time

Re: Newton's rings (?) - Help please.................

Post by sullij1 »

Hi Gordon, Sullij or Joe is fine. Looks like you have got all the information you need to get sorted out. Wishing the best outcome for you.

Joe


Look Up!
User avatar
donboy
Oh, I get it now!
Oh, I get it now!
Posts: 21
Joined: Fri Feb 14, 2014 7:28 pm
Has thanked: 1 time

Re: Newton's rings (?) - Help please.................

Post by donboy »

Gordon,

I use a QHY5L-IIm and experience Newton's Rings with my Quark. I tilt the camera in the diagonal and just about eliminate most of the rings. I just need to add a little more tilt to make them totally vanish. I was thinking that certain diagonals have internal adjustments to align the optical path and maybe using one of those diagonals to tilt the optical path would possibly provide a solution.


Don

Bortle 6.5
AT RC8 CF, Celestron C8, WO 66mm SD Zenithstar, Celestron C80ED, Celestron 102GT, ES 127 FCD100 CF
CEM60, CEM25, AZ Mount Pro
ASI294MC Pro, ASI071MC Pro, ASI1600MM-Cool, Atik 414EXC, QHY5L-IIm, ASI224, ASI290mm, Canon T3i modified
Lunt Herschel Wedge, DayStar Quark

Broadcasting live on www.nightskiesnetwork.com
NSN Channel: HeavensDeclareGod'sGlory

My Solar Album: https://www.flickr.com/photos/23705399@ ... 5393470230
My Astro Albums: https://www.flickr.com/photos/23705399@N04
User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17948
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Been thanked: 1 time
Contact:

Re: Newton's rings (?) - Help please.................

Post by swisswalter »

Gordon Ewen wrote:
..... Since then I have been using the poly bag method but this dimmed the image so much I had been adjusting the exposure and/or gain. REgards ......
Gordon
Hi Gordon

do not use the polybags, the clear polyehtylene food foil in the kitchen does a much better job


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
User avatar
grimble_cornet
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3537
Joined: Tue Jul 10, 2012 5:10 pm
Location: UK West Midlands
Been thanked: 47 times

Re: Newton's rings (?) - Help please.................

Post by grimble_cornet »

Agreed Walter, I use 'Clingfilm' food wrap to produce solar flats and get far better results than when using the de-focusing method which I find can actually make things worse :lol:

John, the Cortner modification of the tilt adapter (which is now on the ZWO website discussion group page) required a 5.7 degree tilt for the ZWOASI120MM to be ring free so your experience confirms his results :P


.

.



.


Mike Garbett

Selection of Solar and Deep Sky images on Flickr: https://www.flickr.com/photos/mikegarbett/
User avatar
Gordon Ewen
Almost There...
Almost There...
Posts: 539
Joined: Sun Apr 20, 2014 10:15 am
Location: Moggerhanger, UK
Been thanked: 257 times
Contact:

Re: Newton's rings (?) - Help please.................

Post by Gordon Ewen »

Thanks for the further comments. I was out again this morning - new post- and got some interesting results. Using a 2x Barlow I could see the Newtons rings as usual on the laptop screen, but after processing without a flat they were just about invisible on the final images; great, but a little puzzling. I did try flats again using the same settings as for my video, but Autostakkert didn't remove the rings.
I also saw the rings when using a Ca filter and Baader solar film on my 120 refractor. Seeing was so bad the images were awful, so no you can't look at them!
I'll have to order some more screws to get a bigger offset on the tilt adapter.
Gordon


Lunt 152 DSII Ha scope, Orion Optics 12" ODK, C9.25
Skywatcher EQ8 x 2
Lunt 1 1/4" Herschel Wedge, 2x,3x Barlow, 5x Powermate, Baader Ca filter and solar film.
https://www.flickr.com/photos/74614447@N02/
Post Reply