[QUOTE=Don Pensack]Note that 1nm = 10 Angstroms.
An H-alpha filter that's usable for solar viewing has a maximum bandwidth of 1 Angstrom (like the PST), or 0.1nm.
QUOTE]
Whoops! Yes, sorry. It was late at night. (That's my excuse - it wasn't the night-cap...) Yes in some places it should have been Ångstrom where 1 Å = 10E-10 metres, although this is now no longer a 'real' unit and has been officially dropped and we are now all suppose to the SI unit, the nm = 10E-9 m.
So to correct what I wrote - the Baader 7 nm (70 Ångstrom) filter and other similar filters are useless for solar prominence and flare etc observation, even when correctly filtered with other blocking filters. For prominences and flares etc, you need at least 10 Ångstrom - preferably much less - and for granulation you need a 0.1 nm (1 Ångstrom ) or less filter, although the good stuff isn't really visible until you are down to at least 0.7 Ångstrom, as Don points out.
The easiest and cheapest way that I know to get reasonable performance is to strip a PST and put the black box on a better scope.
A problem with most of the sub-Ångstrom filters are that they only work at large f numbers - typically f10 or preferably more. The angle at which the light comes through the filter is too great on slower telescopes and due to the thickness of the film and the optics of the filter, the bandwidth of the filter increases and you lose the sub-Ångstrom filtering capability. What you tend to get on a telescope that is too fast (ie the light coming down is to convergent) is a donut area of the image where it is OK and the rest of the image is outside the H-alpha wavelength.
'Tuning' of the filter is usually done by tilting the filter - which changes the effective thickness of the film.
The other way is to build yourself a solar spectroheliograph. You can do this for about $1000 - $1500 and a month of Sundaze. Basically it uses a diffraction grating, other optics and a slit and a rotating element to tune to the H-alpha - or any other frequency - you want.
There are a few websites devoted to this topic. A guy by the name of Veio has written a lot about them and you can download his book as a PDF. Also Westland and there are others. Have a look halfway down
http://www.digilife.be/club/Franky.Dubois/sit.htm and there are links to a number of sites.