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Using a Nightime H-Alpha filter for Solar viewing?

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#26 ken hubal

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Posted 06 December 2010 - 06:24 PM

One simple word to sum this up...DON'T!!!
 

#27 Doc Willie

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Posted 10 January 2011 - 03:20 PM

Well most of us are thinking of using the H filter WITH a white light filter. Your warning is, however, warranted.

Then the next question is, what about stacking an OIII filter with a UHC, and may even a SkyGlow filter behind the white filter?

A cursory look at the explanations and tables above suggests that it won't work.
 

#28 Don W

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Posted 10 January 2011 - 03:30 PM

The bottom line is this. If it were that easy we'd all be doing it already. But it's not. The mixing of other types of astronomical filters will NOT prevent the harmful radiation of the sun from entering your eyes. Period. Don't do it!!!
 

#29 Doc Willie

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Posted 10 January 2011 - 08:01 PM

I SAID behind the white light filter. Not gonna consider otherwise.

If it worked 25% as well as dedicated solar scopes, it would still be worth me doing, and would still be worth your buying the good stuff.
 

#30 Don W

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Posted 10 January 2011 - 08:15 PM

Putting some sort of filter behind the White Light Solar filter will not show you any H-Alpha features. What do you think it will do?
 

#31 brianb11213

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Posted 11 January 2011 - 04:18 AM

What do you think it will do?

I would expect a "broad band" Ha filter (used in conjunction with a "white light" filter of adequate density to provide protection) to give a view very similar to that which I enjoy using an ordinary deep red (Wratten #29) filter. A great "white light" view with significant steadying of the seeing compared with the usual green, but no Ha features at all - unless perhaps an unusually strong flare was in progress.
 

#32 David Knisely

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Posted 11 January 2011 - 03:14 PM

Hi there. You posted:

I SAID behind the white light filter. Not gonna consider otherwise.

If it worked 25% as well as dedicated solar scopes, it would still be worth me doing, and would still be worth your buying the good stuff.


Unfortunately, it won't work. The passband width of even imaging H-alpha filters (those used for emission nebulae) have a band width of between 30 and 100 angstroms (FWHM). This is much much too broad to see any solar H-alpha detail, as you need something around 1.5 angstroms or less just to pick up the prominences without an occulting disk being used. To get chromospheric disk detail requires a passband that is less than one angstrom wide, so again, adding the H-alpha "nebula" filter after a white light filter just won't work. The other factor which impacts things is brightness. H-alpha solar detail is quite faint, and when you run it through a typical white light solar filter, it will become too faint to see easily even if the second H-alpha filter was narrow enough. Basically, we are stuck with using the standard (and somewhat expensive) Fabry-Perot etalon-based H-alpha solar filters if we want to see something other than white light detail. Clear skies to you.
 

#33 Doc Willie

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Posted 11 January 2011 - 11:44 PM

Unfortunately, it won't work. The passband width of even imaging H-alpha filters (those used for emission nebulae) have a band width of between 30 and 100 angstroms (FWHM). This is much much too broad to see any solar H-alpha detail, as you need something around 1.5 angstroms or less just to pick up the prominences without an occulting disk being used. To get chromospheric disk detail requires a passband that is less than one angstrom wide, so again, adding the H-alpha "nebula" filter after a white light filter just won't work.


I unnerstand now. Thanks for your patience in explaining this to a newbie.

One angstom passband. That is about as astounding as the scale of interstellar and intergalactic distances.
 

#34 BYoesle

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Posted 12 January 2011 - 08:42 AM

As noted above, beyond the passband issues of the night-time nebula filter, the reason you really can’t use a white light filter in conjunction with such a broad-band nebula filter is that the white light filter will render the chromosphere and prominences completely invisible.

Under “normal” conditions, it takes a total eclipse by the moon to block out the hundreds of thousands as times brighter photosphere to view the prominences around the edge of the sun. If you use a standard white light filter as required to reduce the photosphere’s brightness to a safe level, then you’re also reducing the brightness of the chromosphere by the same amount. Even if you used and occulting disc to simulate an eclipse, and had a proper narrow band filter to view the prominences (or the disc itself), this wavelength of light will have been reduced in brightness by the same amount as the photosphere, and therefore the chromosphere will be totally invisible.

Solar H alpha filters are indeed expensive. But the technology required to render the photosphere invisible and allow only the light from the chromosphere safely through is incredibly complicated and requires unbelievable tolerances. On the other hand, nothing else you can observe with a telescope is as awesome and inspiring to witness as a solar flare, eruptive prominence, or the beautifully mesmerizing clouds of glowing hydrogen that are constantly changing…
 

#35 attckbvr

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Posted 12 January 2011 - 11:54 AM

Amen Bob! well said!
 

#36 Doc Willie

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Posted 12 January 2011 - 03:13 PM

As I said, you need eight telescopes.
 

#37 RodgerHouTex

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Posted 21 February 2011 - 01:53 PM

There are alternatives to etalons though right. I seem to recall seeing prominence photos etc. long before etalons existed as far as I recall. Didn't folks back then use a spectrohelioscope? I believe the principal was to gather light with an objective, focus it on a slit, and then tune another slit to the frequency you wanted and then reexpand it to a disk using another lens. Or something like that?
 

#38 colinsk

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Posted 22 February 2011 - 12:10 AM

Spectrohelioscopes are great as you can tune them to any frequency. However that are quite complicated. Look up Fred Vieo's book that is online for free to learn about the technology.

http://www.spectrohelioscope.org/

Then there are Lyott filters that can have a much narrower bandwidth than an etalon that use the birefringence of quartz or calcite. There are even tunable Lyott filters that consist af many crystals and polarization elements.

http://en.wikipedia....iki/Lyot_filter
 

#39 Don W

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Posted 22 February 2011 - 07:21 AM

Ok, this has nothing to do with the subject or purpose of this thread. Please start another one.
 

#40 Scott in NC

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Posted 23 April 2014 - 03:17 PM

For a continuation of this thread, please see Part 2 here.
 






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