I would like to add that I
have found that the Lumicon and Thousand Oaks OIII filters work better
for
me on scopes greater than 8", as on scopes 8" and less they seem too
dark.

Well, I have successfully used the OIII on scopes as small as 60mm as long
as
the power range is kept low (4x to 10x per inch of aperture). Indeed, I
have
often used the OIII on M42, M8, the Veil, the North America (NGC 7000),
the
Helix (NGC 7293), and a few other targets with my little 80mm f/5
refractor.
However, the reason that most people think the OIII doesn't work as well
for
smaller apertures is because the number of objects which those apertures
can
easily reach (and which the OIII is capable of helping) is somewhat
limited.
It does produce a dark field, but with proper dark adapation, a benefit
can
still be gotten from the OIII in smaller apertures (and amateurs will
still
want to have the OIII around when they upgrade to a larger scope).


I see your point about the OIII and smaller apertures. Maybe for me it is
not so much the the OIII is too dark, but that it dims stars. For instance,
I really like how the open cluster NGC6530 looks in M8, and I find that in
anything smaller than 10" the OIII pretty much kills it. I really like the
OIII in the 10", and in this scope I find I use it more than the UHC.

Dennis