(IAAC) Re: Using O III with higher magnifications ?

Alister Ling wrote:
>There are some rare exceptions, but straight visual appears to be the best.

I agree with Alister's comments regarding the OIII and extragalactic HIIs.
In exploring the smaller emission regions visible in M33, M101, NGC 2403,
and other targets, I found the OIII rarely gave any noticeable advantage.

But I was surprised to hear Alister feels the same about the UHC! I recall
in particular in M33, being amazed at the result: in a 20" f/5 at 210x with
a UHC, the outer arms of the galaxy were far less prominent, and yet still
I could trace several of them merely by following the subtle arcs of tiny,
nearly-stellar HII regions along them! Such "stellarings" (as Brian Skiff
so nicely called them) were probably still visible without filtering, but
I would have been hard-pressed to ferret many of them out from the ambient
glow of unresolved stars in M33's arms.

Clear skies,
Lew Gramer

Internet Amateur Astronomers Catalog of Deep-Sky Observations:

To UNSUBSCRIBE from the 'netastrocatalog' lists, use the Web form at: