Newton Rings

[Dunc78]

Hello, sorry if this is in the wrong section. Iv just got back into solar imaging with a Lunt LS50THa and Asi 120mm mini, now I never used to get newton Rings with my old pst. What gives the most sucessfull end result flats or a tilt adapter? I'm assuming not having them to start with is the way to go. Now where in my lint pic would the tilt adapter fit in as the back focus etc is critical. Also what's is the best method of taking solar flats? I see sharpcap has a flats sections but it's paid for. Has anyone used this and is it worth purchasing. ? 

[Elp]

As far as I know flats won't help with the newton rings, you need a tilt adjuster.

Not familiar with Lunt, are filters contained within the diagonal as that will dictate whether you can image straight through without the diagonal, that would allow you to fit spacers and a tilt adjuster.

I believe you can take flats whenever as long as you don't alter the train at all (focus, camera orientation etc).

[Dunc78]

Hi Elp, yes filters in the B600 diagonal. 

[Hughsie]

The tilt adapter would sit between the camera and diagonal. Typically the camera screws into one side of the tilt adapter and a 1.25” nose piece would screw into the other. The nose piece is then inserted into the diagonal. 

You have two potential issues. 1) the asi120 is prone to newton rings. Even with a tilt adapter there are comments on other forums where even the maximum tilt in the adapter wasn’t enough to remove them. 2) I haven’t seen a tilt adapter that fits a mini version of the asi cameras. That’s not to say there isn’t one, I just haven’t seen one.

Like Elp, I am of the opinion that flats will not calibrate out Newton Rings this is because they appear in the flats too. To capture flats I would point the Lunt towards the centre of the Sun, remain in focus and put an opaque plastic bag over the front of the scope secured by an elastic band. Something like a crumpled sandwich or freezer bag works but it needs to be clear/whiteish. Pull the bag tight. Then adjust your exposure time so that the histogram peaks around the 50% mark and capture your frames, say 100 in SER format.

In Autostakkert you can create a master flat and open the SER file. Autostakkert will then stack and produce a master flat in tiff format which you can then load into Autostakkert to calibrate your images.

Hope that helps.

John

 

[Dunc78]

Thanks Hughsie, I. Just noticed the front lens part of the Asi 120mm screws off. Will try it next sunshine we get but are the internal reflections coming from the Lunt optical train or does the camera lens window also add newtons rings? It would be quickly swapped into the Lunt eyepiece so little chance of dust. 

Anyone tried this? 

[Anne S]

Could the single screw in the eyepiece holder cause some newtons rings? I remove the eyepiece holder and attach my Hypercam 178 to the revealed T thread. That's the only way I can get focus! I do need to use a spacer as well as I've a Starlight focuser with very limited focus range. It's much better than the original helical focuser.