H-alpha filters

Who makes these, and approximately how much do they cost? I've looked around, and have not found much information regarding these solar filters.

Check out the Coronado website: http://www.coronadofilters.com/


Sit down before you look at the prices :-0



Jeff

Depends on what you want to use it for!

H-a refers to a very precise frequency... 6562.8 angstroms (so-named for the first Hydrogen emmision line in a star's spectra... hence Hydrogen-alpha).

The tighter the bandwidth (spread), the more contrasty the effects, but also progressively far more expensive for a given size.

H-a filters typically range from 1 1/4" on up in diameter and 10 angstrom down to 0.2 angstrom, with the former being used for imaging of H-a rich nebular areas of starfields and the latter for solar observation. If intended for solar use, a spread up to about 4 angstrom will show the prominences with detail and fullness, but no surface detail (above 3 or 4 ang the proms start to lose detail). Surface detail starts to really take off about <0.7 angstrom and is incredible at <0.2 angstrom (see David G's image posted here):

http://www.astromart.com/messages.asp?message_id=70939&page=

Prominences take on a thinner appearance at that level though, as they tend to billow towards and away from us at tremendous speeds, causing blue and red shifting from the main-band frequency. Thus many actually prefer a <0.5 or <0.7 angstrom filter, so as to capture the fullness of prominences as well as surface detail. Of course "seeing" will affect the ability to pick out detail on the sun as it does also with night time targets.

FWIW, to put the level of precision of these filters in perpsective, 1 angstrom is one hundred-millionth of a centimeter!

So... what kind of views do you have in mind? If for promnences, a very capable prominence-scope can be constructed for about $300 (link on the bottom of the page):

http://www.astro-nut.com/stella2002p_151.html

Paul

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