Solar film filter and h-alpha filter

[Leigh]

Hi,

I have seen white images of the sun achieved by using a Baader solar film filter and also h-alpha images of the sun.

What view/images would you expect from using both the sun film filter and a h-alpha filer in the eye piece at the same time. Would these two filters work well together?

Thanks,

Leigh

[Demonperformer]

The problem would probably be that a proper Ha scope has a much narrower band width than a standard (narrowband) Ha filter, so probably would not be too good.

[Merlin66]

Unfortunately it doesn't work like that...

You'd end up with a "red" white light view - and still just see the sunspots etc.

Solar Ha observing is completely different from Ha imaging of deep sky objects.

The Ha solar filters are VERY expensive and have an extremely narrow band (1A = 0.1nm)

[Leigh]

Thanks for your replies.

7nm is not quite narrow enough then

I have ordered a solar film filter so just curious what to expect from it apart from the white and sunpots (Which I'm looking forward to seeing!).

Thanks

[Stephen]

I find a continuum filter helps improve contrast on white light solar observing : a cheaper option may be a dark green wratten filter.

[John]

I use a white light filter occasionally with my 4" refractor. It shows sunspot structure, surface granulation (depends on viewing conditions) and faculae pretty well. Mine is a commercial on that uses the Baader film.

[Leigh]

Thats good to know, I was hoping I would see surface granulation.

I don't have a continuum filter but I'll give the green a go.

Fingers crossed it'll arrive tomorrow

[arbacia]

The short answer is: a Deep Sky H alfa filter is not valid.

The solar H alpha telescopes have a sub-Angstrom wide band. PST about 1 Å, Solarmax, Lunt about <0,7Å. If the H alfa band is broader we can not get enough contrast as the non H alpha red light floods the image.

Deep Sky H alpha filters are intended to grab the H alpha light from where no other red light comes. So, they have a band of 15nm to 7nm (more or less). Although this filters are narrow band, they are too broad as to permit a complete fllooding of red light in the image and therefore the H alfa signal is completely lost.

Someone in Spain made H alfa coronographers with a central obstruction and two deep Sky H alpha filters that can be tunned by tilting them slightly. Protuberances can be seen with it. This telescope cell is very complex to made and should be regarded as a "scientific workshop" item.

Patricio

[E621Keith]

I may be totally wrong but I read somewhere H-a in the sun is actually absorption line rather than emission line. It is produced when continuum sun light from the photosphere get absorbed by the hydrogen in the chromosphere. Solar H-a filters show the lack of light at H-a by cutting the continuum light transmission to a level where the light lost at Ha becomes significant. The narrower the band pass, the less continuum light will pass, the greater the darkening at Ha, and the greater the contrast.

Ha in nebulae are emission lines where light is emitted in Ha. Since there are no other light sources, the Ha line dominates, so there are no need for a night time Ha filter to have an extremely narrow band pass.

If you tried to use a night time Ha filter for solar, it would pass too much light from the continuum spectrum and you will not be able to notice the darkening associated with absorption at the solar Ha line.

Anyway, a night time Ha filter + white light solar filter will not be able to show you any Ha feature. It will only make the image red.

[arbacia]

What we see with a Solar H alpha filter is the Chromosphere as it emitts in H alpha line. The Photosphere is what we see in white light.

The Chromosphere is very hot (20,000ºC, Photosphere is "only" 6,000ºC). At that temperature the Hydrogen emits in the H alpha emission line. What appears dark are the spicules and filaments. In this red emitting layer we see cooler materials, as they are not emitiing in H alfa , they appear darker such as spicules and filamets .

Patricio

[Leigh]

Thank you for the detailed explanation. I had to read through this a couple of times to absorb this but I think I've got it

Thanks,

Leigh

[markt]

Hi,

I have seen white images of the sun achieved by using a Baader solar film filter and also h-alpha images of the sun.

What view/images would you expect from using both the sun film filter and a h-alpha filer in the eye piece at the same time. Would these two filters work well together?

Thanks,

Leigh

Hi Leigh.

For visual work I would not recommend Baader solar film and the 7nm halpha filter. All this will do is provide a very deep red image of the sun that you will struggle to see the finer details...

However, using this combination of filters for imaging with a mono ccd camera will produce some very detailed results once you master the process...

Mark

[Leigh]

Thanks for the advice Mark and sorry for my late reply.

So this combination in mono would produce good results?

[markt]

So this combination in mono would produce good results?

Yes, but will not be a Ha view, will be a whitelight view in deep red wavelengths - if that makes sense...

[E621Keith]

So this combination in mono would produce good results?

I think if you use an achromatic refractor, a night time Ha filter will eliminate chromatic aberration and make the sun deep red. That's about it.

[Merlin66]

A baader Continuum or green filter actually gives better contrast for visual observing with a Solar Film.

[Leigh]

I checked my solar film filter before trying it out for the first time this morning. Although no holes were visible, when I held it up to the sun, there were very small pin holes only seen because of the sun coming through them. They are very small but I guess this means the filter is no good and too dangerous to try?

If this is the case I will need to get some more film.

[Merlin66]

Leigh,

No the filter will still be OK.

If the "very small pin holes" were only visible against the bright solar disk, then all that'll happen is you loose a little contrast.

It's still 100% safe to use.

[Leigh]

Thats good to know, thank you.

I packed it all away quite disappointed yesterday. Nice clear sky today so I'll set it up again. I don't have a continuum filter but do have the green to try.

Thanks for all your help and advice