3 replies to this topic

[chrishalpha2017]

Hello,

as some of you know already I watch the solar prominences with a spectro-coronagraph (a coronagraph where the h alpha filter is replaced by a diffraction grating).
Two days ago I bought a 12 nanometer Ha filter for some experiments in my spectro. I used to use a high pass filter to isolate roughly the Ha from the rest of the spectrum. A red filter for the deep sky observation of around 60 -70 nm bandwidth ( 600-700 Angstroms).
Of course these kind of filters are not at all suited for solar observations as its far too dangerous for the eyes and the prominences wont be seen.

Still , I set my 12nm filter in the ASI 178MM and started to look for the Ha line on the screen of my laptop as I was starting my session of prominence observation this afternoon with this new filter.

Accidentally I first found the zero order of diffraction and on the screen appeared the image of the entrance slit of the spectro coronagraph. The LYOT stop was set properly in order to stop the instrumental light diffusion and then enhance the contrast.

Here is what I saw on the screen :

 

 

 

 

So, in fact I could see the solar prominences with a 120 angstroms H alpha filter . I could see them with the CAMERA ONLY.

I tried visually and the prominence was visible but the contrast was much lower than the image with the camera.

I then tried (with the camera) with the wide band filter and no prominences could be seen.

Its suprising to be able to do that  as usually the sky in Paris is so hazy that it s not supposed to allow this kind of observations with such a filter.

Here are the photos with my spectro coronagraph and the 1200 l/mm grating.

 

 

 

Chris

Edited by chrishalpha2017, 26 May 2023 - 04:27 PM.

[Klaus_160]

Nice images!

 

I have found that any h-alpha interference filter will show prominences in a Coronagraph unless the sky is really bad.

 

When using a colored glass filter the sky needs to be good, and to see something without a filter the sky needs to be near coronal quality.

 

Here is an example of a prominence in a Coronagraph without a filter:

 

 

Also see here for a comparison:

 

https://www.cloudyni...ve-prominences/

 

 

 

And yes, absolutely camera only! Even the interference filters do not block above 1000nm-1100nmn letting the dangerous near IR pass!

 

 

Klaus

 

 

[John_Moore]

Great captures, Chris...they remind me of Sprites we sometimes see during lightning occurrences.

 

John

[chrishalpha2017]

Thanks guys

 

 

Nice images!

 

I have found that any h-alpha interference filter will show prominences in a Coronagraph unless the sky is really bad.

 

https://www.cloudyni...ve-prominences/

 

 

Klaus

I tried with the Lumicon #29 and I couldnt record prominences. I guess the sky wasnt good enough ^^.  An then I "played" with the lyot stop and it makes a huge difference. 

 

As I have also a color cam I think i'll give it a try to show what I get   Still , my best results are with the grating.  I initially bought this h alpha filter because I'm making a annular entrance slit wich will allow me to check the solar limb in one go  to find the most interesting prominences .  If I use a Lumicon #29  I get 2 spectrum overlapping as each edges creates its own spectrum. But with a 12nm (or less) is used then both h alpha lines  are separated by a black gap and the contrast isnt lowered.

 

I'll post pictures once Its finished.