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When a star is too faint to activate cones in the retina, it will appear colorless, which the brain interprets as white or gray.
Bright stars, however, will activate cones and you will see colors, as we do with Betelgeuse or Antares, etc.
When a filter passes only the blue-green, as with the TeleVue BandMate II Nebustar or Lumicon UHC Gen.3, if a star is bright enough to activate cones, it will appear blue-green if any color is seen at all.
The Astronomik UHC visual also passes a broad swath of red, so some red flaring will occur when looking at a star if the star is bright enough.
The DGM NPB passes the red, but includes some shorter wavelength orange, so if color is seen in the stars, the stars appear red orange because the majority of light passed by the filter is in the red-orange with only a narrow sliver in the blue-green. The DGM NPB has about the narrowest bandwidth in the blue green available in UHC-type filters today, at around 22nm.
Older TeleVues (pre 2018) were wider, as were older Astronomiks (pre 2016), but you have to go back to pre-2001 to see any red in Lumicon UHCs.
I've used all of these extensively on nebulae over the last 3 years, as well as 48 other nebula filters.
Where O-III filters are concerned, the TeleVue and Astronomik are now pretty much identical, as is the ICS filter. They are all made by Astronomik. The Lumicon is made in the US, but has a nearly identical bandpass to the others.
The DGM is wider and doesn't offer the contrast of those others. Baader and Thousand Oaks are single-line O-III filters and more appropriate to imaging.
As is the case with the UHC-type filters (where 45-50nm bandwidths predominate), most of the Chinese O-III filters are very wide, with bandwidths of 25-28nm quite common. Had their bandwidths been placed differently in the spectrum, they'd have been high-end UHC-type filters, but their bandpasses miss the H-ß line.
With the bandpasses common in the better UHC-type and O-III filters today, the contrast enhancement of the UHC-type filters runs about 2.5 magnitudes, with the narrower O-III filters yielding about 3 magnitudes.
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