Re: (IAAC) Markarian 205 - 8inch F/10
Welcome back, Nick!
You are right - the views of many objects are worsened by narrowband filters. I
guess I was proposing that the reason for those worsened views was generally
just reduced light transmission overall - rather than any reduced contrast of
the object/feature relative to background. But I wonder if there may be areas
of some of these nebulae (Cat's Eye in particular) which do in fact emit their
light mainly at wavelengths outside the Hbeta and OIII regions?
One thing for certain, there are lots of "emission" nebulae whose light is
actually more than half reflected (continuum) starlight: using even a wideband
filter on these can make them disappear entirely (or make many of their
features - the primarily reflected ones - disappear from the object).
As a matter of fact, one of my favorite observing projects is trying to
distinguish and map out the complex, intermingled dust- and gas-heavy
components of brighter nebulae, using nothing but "UHC blinking".