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confusion on bandwidth
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.
Larger telescopes need 0.7 Angstroms, or .07 nm in order to be dark enough.
If doing H-Alpha at larger aperture, bandwidths get down to ~0.2 Angstroms, or 0.02 nm.
When 0.7 Angstrom H-Alpha filters are used on larger telescopes, they typically stop the scope down to 90mm or so.
A 7nm H-alpha filter is passing 70 Angstroms, and this is simply not safe for viewing on any size scope.
I've seen some H-Alpha filters that are simply a long-wavelength pass filter, and this style will not work well photographically with modern CCD cameras unless an IR filter is added.
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