Ha Solar imaging Newtons rings woes

[tich]

Afternoon all well the title of the thread says it all really so I was wondering if some of you more experienced Solar imagers could help, I will admit I've only done a small amount of Ha my first attempt was last Sunday before the Mercury transit so very limited at best. I am using quite a modest set up, Lunt 35 Ha basic solar scope & an ASI 120 MM mono camera although the ASI's from what I've heard suffer badly with Newtons rings so I might be looking at getting a camera that doesn't suffer with them. (If there is such a thing) Of course budget will enter into it although buying used has never been an issue with me.
Now I have heard of tiltling the ASI camera but from what I've read it needs to be tilted at around 6 degrees, which to me sounds quite a lot & I would think you wouldn't be able to achieve focus right across the field, of course please correct me if I'm wrong.

You can see on these images from my failed mosaic the king of thing I'm getting but I only get it in Ha & not white light using the same Barlow lens.



The same again in white light using the same camera & 2X Barlow lens using a Lunt wedge & ED80.

[Davey-T]

Hi Tich, did you take flats ? you can use them in AS2.

I've just bought a tilt adjuster to try and combat uneven illumination, may even get to try it if the clouds go away

Dave

[tich]

Good luck Dave & please post the results as I'd be very interested to see & hear about them. My only niggle would I still have enough focus to mess around with if i brought one for myself? As there just isn't enough inward focus with the Lunt so I'm having to use the 2X Barlow lens to achieve it, tried a reducer but that didn't work either but then I did say I'm new to Ha imaging, so it's a whole new can of worms for me to open lol.

As for flats no I haven't took any, I did read a guide on how to do it all seemed a bit baffling to me lol, mind you I think you would have to take them straight after taking the lights so the tracking would need to be good to I'd imagine.

 

[Davey-T]

I've tried one of those thin plastic bags they use for veggies in the supermarket and cling film over the end of the scope, I've found cling film works best for me, just wrap round the scope up the exposure to compensate and take a 500 frame video then turn it into a flat in AS2, doesn't  always work but that's probably my fault

Dave

[Drop Of Sun]

I think the Point Grey CCD's are less prone to Newton's Rings, I'm not up to speed on their latest cameras, they had some good options at I think £300 or less a while back brand new. My ZWO ASI174 CMOS is a bit prone to Newton's Rings, with my Quark and 120mm scope I found it best to take multiple flats over the session, if there was a big gap between the flat and the main image, I found sometimes the rings were out of synch and I got twice as many rings!!  That was my experience, anyway!

I found it okay to take multiple flats, especially using the cling film or a bag flat, no need to adjust focus, the bag or cling film magically does the blur for you

Another option is to get a large sensor camera and let the image drfit over the chip, that should get rid of the rings and any dust bunnies.

re: tilting I saw a few images done with quite a big chip (ASI174) that looked good to me, however, I wonder if how much you have to tilt varies?? Some people seem to get stronger rings than others with the same gear! I need to do some more tests, but so far, the Quark I am using now seems less prone to Newton's rings with with ASI174 than the Quark I used to use?!

[Davey-T]

My PG Blackfly gets Newton rings without a .5x focal reducer but not with one ?

Dave

[tich]

You'd think with today's coatings they devise some sort of filter to stop the internal reflections, or am I barking up the wrong tree. Unfortunately with a 0.5 reducer fitted I can't achieve focus at all which is some what annoying as I'd rather image more of the disc rather than getting to close if that makes sense.
Cheers for the replies & help so far.
 

[Zakalwe]

NRs will happen when imaging in narrow-band when using some CMOS cameras. They are there in white-light too, but are much, much fainter as the multiple frequencies of light will interfere with each other. In narrowband you do not get this and the NRs are highly visible. They are a symptom of using todays fast frame rate cameras.

A tilt-adapter from Rowan Astronomy will kill them stone dead. Flats can work, but I found that on my ASI 174 camera I also get really bad banding with over and under exposes parts of the image. Flats can't sort this out.

[Macavity]

Didn't get anywhere fast with "cling film" (Tesco or Morrisons!) flats. As mentioned elsewhere, found
a workable solution by "stopping" tracking during the exposure. Or rather more exactly by adjusting
the speed within EQmod by [+/10%] of the default rate via EQmod's "Custom Rate" dialog box... 

Background artifacts, such as NRs, are then "blurred out" by the stacking software. 
Clearly not the only way, but one readily accessible within many standard setups.

[Zakalwe]

You have to ramp the exposure right up when doing cling-film flats. Increasing the exposure is no problem as the system just wants the luminance values from the optical system. Don't be afraid to take the exposure times as high as they need to be to allow you to get a couple of hundred frames to stack.

[Mick J]

You may have seen this tich, page 3 of ChrisLX200's thread in the diy has homemade tilt and some discussion, hope this helps.

[tich]

10 hours ago, Zakalwe said:

NRs will happen when imaging in narrow-band when using some CMOS cameras. They are there in white-light too, but are much, much fainter as the multiple frequencies of light will interfere with each other. In narrowband you do not get this and the NRs are highly visible. They are a symptom of using todays fast frame rate cameras.

A tilt-adapter from Rowan Astronomy will kill them stone dead. Flats can work, but I found that on my ASI 174 camera I also get really bad banding with over and under exposes parts of the image. Flats can't sort this out.

Cheers mate, by what I've read the ASI120 MM I use can need up to 6 degrees of tilt & the Rowan one goes up to 8 degrees so looks promising. I've just emailed them to see how much more length it puts onto the imaging train as getting my set up to focus is pretty tight,  I can only achieve it by screwing a Barlow lens onto the camera's nosepiece due to not having enough inward focus.
 

[Owmuchonomy]

Interesting thread. I haven't as far as I know suffered this problem with my ASI 174 and Lunt 60. My blocking filter has gone away to be cleaned so it's only been used once.  One observation I will make is that I used the combination in Alt Az mode for the recent transit.

[Davey-T]

If I had a Lunt LS35 that doesn't have enough inward focus travel I'd be inclined to chop a bit of the back of the tube as long as it doesn't compromise it in any way, can't see why it would be a problem or why it's not made with more inward travel as it's easy enough to add more.

Dave

[tich]

3 hours ago, Davey-T said:

If I had a Lunt LS35 that doesn't have enough inward focus travel I'd be inclined to chop a bit of the back of the tube as long as it doesn't compromise it in any way, can't see why it would be a problem or why it's not made with more inward travel as it's easy enough to add more.

Dave

I totally agree, the way it focuses is odd by twisting the end of the diagonal  & there's no way of locking it, a simple R&P focuser would be better in my opinion, but I can't complain to much I guess as it's my first Ha scope. I did read a write up online I'd imagine when these were first made & apparently Lunt said they would make the tube a bit shorter because of this issue but it looks like they didn't.

[Macavity]

For me, producing FLATS with the helicoid focusser requires to big a TWIST to
give e.g. defocussed images - Moves the Image on the chip! Cling file seems to
produce a fair bit of light scatter / distortion? Or I wasn't that enthusiastic?

Personally, I don't find the current Helicoid focusser THAT bad! It might be
possible to find a low-profile Crayford focusser, but I'm not sure if I want to
(can!) continue pouring money into yet another seemingly bottomless pit. 

Never know where to post these things (There may simply be NO interest! lol)
But I have vague long term ideas re. alternative focussers for my Lunt50THa:

https://stargazerslounge.com/topic/270412-35x05mm-adapter-for-lunt-ls50tha-found/

The above will adapt the "back end" to a standard T2 "whatever" as a start!
Just wish Lunt would have provided a straight through non-diagonal BF... 

[Zakalwe]

28 minutes ago, Macavity said:

Cling file seems to
produce a fair bit of light scatter / distortion? Or I wasn't that enthusiastic?

 

That's exactly whats required.

I cling-film the front of the scope (I only do it when using the Quark as the disc fills the FoV) and then de-focus. Ramp the exposure up to get the histogram at about 60% and fire off a couple of hundred frames.

 

I've also seen a home made tilt adapter that doesn't need a 3d printer. Two bits of 6mm plywood or MDF with some soft foam glued into a sandwich. Run some bolts through each corner to allow adjustment and hey-presto, the cheapest tilt-adapter going!

[Macavity]

27 minutes ago, Zakalwe said:

I've also seen a home made tilt adapter that doesn't need a 3d printer. Two bits of 6mm plywood or MDF with some soft foam glued into a sandwich. Run some bolts through each corner to allow adjustment and hey-presto, the cheapest tilt-adapter going!

Ah, a fellow enthusiast for the MDF Anulus? (The only real purpose for "DIY Hole Saws") 
I certainly think it is far better to have something (fairly resilient) that SQUISHES than the
awkward push-pull arrangement in "collimators" (large or small) finder brackets etc. etc. 

Cling Film showed some promise. I didn't do it properly! I found (as anecdotally) that it
works better with close-up, part disks, rather than isolated FULL disks over a "black" sky.  

[Davey-T]

Here's a flat done with cling film, PGBFly camera, not altering the focus just upping the exposure and an image with it applied.

Dave

[Zakalwe]

Here's the difference that tilting can make:

ASI 174 camera screwed onto a Quark. Lots of NRs and horizontal banding. Uneven field illumination as well. This was created by de-focusing the camera and using cling-film over the scope objective.

 

After fitting the tilt adapter. I kept the tilt angle as small as possible to prevent focus problems. There's a tiny hint of NRs left, but they calibrate out perfectly.

 

[Davey-T]

Here's an image with the flat applied, still some evidence of NRs on the left, and uneven illumination.

Dave.

[Lowjiber]

I'll just relay my experiences...

I have an ASI120MM that suffered from NRs right outta the box.  I used flats for about a month made using a ziplock bag over the scope.  Flats work, but are a real pain when capturing.

I bought a Telskopp Tilt-Adapter and was able to eliminate them by putting the maximum tilt on the adapter and placing the tilted axis along the longer dimension of the chip.  I did get some uneven illumination, but not something that couldn't be solved in Photoshop.

My ASI174, is fortunately NR-free, but it does exhibit a slight bit of uneven illumination.  However, again it is easily dealt with in Photoshop.

To cure uneven illumination in PS...

Use the Lasso Tool set at 200 pixels to select the area of uneven illumination.  Then use a Levels Layer to darken the bright area... adjusting the right-hand Output slider.  Usually about 170-190 will make everything work out.  It takes a little experience and practice, but works great.

Clear Skies

[ArmyAirForce]

On my Lunt LS50, I shortened the optical train by removing the 1.25" nosepiece from the front of the blocking filter, and useing the female thread from a T-ring to join it to the focusser. This then gave me the focus travel to make a tilt adapter for the exit side of the blocking filter. For my ASI120MM, I have 5 degrees of tilt to remove the Newton Rings as seen here. With this setup, I can capture full disc shots with no rings.

If I want close ups, I unscrew the tilt adapter from the blocking filter, fit the M42 eyepiece holder ( supplied ), and unscrew the 1.25" socket from the end of my TAL barlow.

The lens end of the barlow goes inside the 1.25" eyepiece holder......

The tilt adapter with camera then screws on the end....

[Davey-T]

Good solution, Tich has the LS35, does it have the same focuser ?

Dave

[tich]

My focuser is part of the blocking filter & to achieve focus you twist the top of it where you'd put the eyepiece, I did get a reply back from rowan astronomy about the tilt adapter & they reckon it adds another 22mm to the optical train which probably isn't going to do me any favours either.