Re: [APML] o III filter

["Bert Katzung" <katzung1@attbi.com>]

Hi Larry:
Here's the simple answer, I'm sure you'll also get much more expert
answers.....
Remember that filters *subtract* light of certain wavelengths, so the OIII
will increase the *contrast* of an OIII-emitting object vs its background.
It will not make it brighter although it may seem brighter because of the
blacker background.
My experience is that the OIII works great for visual on (for example)  M8
and M42 and does little or nothing on M13 and M31. Because, of course, the
nebulas are heavy OIII emitters, while the cluster and the galaxy are stars
with continuous spectra.
Hope this helps....
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "Larry McManus" <lmcmanus@clearpointadv.com>
To: <astro-photo@seds.org>
Sent: Friday, April 05, 2002 11:49 AM
Subject: [APML] o III filter


> Can anyone give me some information on (o III) filters? Do they
drmatically
> enhance viewing of nebulas and galaxies and are there differences from
> manufacturer to manufacturer? Plus are there any other filters I should be
> considereing when looking at deep sky objects?
>
> Thanks
>
> Larry McManus
>
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