continuing filter-fu

What a useful thread, I'm not kidding. You can see there are TACos
who know what they're talking about. There are places on- and offline
where you'd get a fair amount of nonsense and drivel on this topic.
Not on the one true list. Good info for new folks today, and an
occasion for the grizzled veterans to sharpen their wits.

Sander, you asked about broadband filters. Carter mentioned not
getting much out of his. I did a non-scientific survey a couple of
years ago, asked the smart guys who have been around longer than me,
they all said they don't do much.

Crisp hissef opined ...

>Therefore I'd think the [OIII] filter may be useful in a relatively
>bright sky to let you at least see something that would otherwise be
>drowned out by light pollution. I think in a dark sky site, it would
>make little difference except to darken everything; ie you are
>better off without it in a dark sky site. I would view them
>primarily as a workaround for bright skies.
>right? wrong?

Wrong, but a great implied question. An OIII used visually is real
effective for bringing out sharp details in emission nebulae.
Contrasty views for the big famous ones with the given names, as well
as sharpening the view for objects like Sh2-157. (astro pun
intended). NGC 281, that beautiful EN in Cassiopeia, is great in an
Ultrablock, as is the Flame. Same for planetaries. 246 in Cetus, 40
in Cepheus ... most PN's are fancier in an OIII. All these effects
are pronounced at a real dark site. And as said, an OIII might be the
only way to identify a stellar planetary, by blinking.

Another interesting use of both an OIII and an Ultrablock is that a
reflection nebula won't show any enhancement in either one, the light
from them being not of hot ion emissions but simply reflected
starlight. Good way to separate them out mentally in the dark. M78 in
Orion, for instance, will only get darkened in one of our nebula
filters.

Happy day after Thelonius Monk's birthday,
DDK

-- 
Jamie Dillon <mavericks@No-Spam> <*>
TAC, astro anarchy at work  http://observers.org)
"We now know that nobody lives on Mars,
   at least not year round."  Dave Barry