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When comparing filters between manufacturers, there are a few more specs that would be helpful if known.
Optical density - how well does it block the unwanted (offband) wavelengths, and how far out in to the UV & IR is this rejection valid?
Centre wavelength tolerance - the narrower the filter and faster the focal ratio, the more this becomes a concern.
Transmission percentage - of the desired wavelength.
Transmission profile - does it look like a bell curve or is it mesa shaped (preferable)?
Alluxa is one company that does this. A pity though that they go to the trouble and expense of making a 1nm mesa profiled Ha filter but they have tuned the centre wavelength to the emission line instead of putting it on the shoulder (with the shorter wavelength).
Incidentally, Baader have a 3.5nm filter available now which is a fraction of the cost of the Astrodon (3nm)
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