Excellent Richard. Thanks alot. You answered more than what I asked, but
what I wanted to know really, but was a bit embarrassed to ask. And that
was exactly what filters can I actually see the results. I keep seeing your
remarkable photo efforts, and each time I kept wondering what my naked eye
could see if I was looking at it thru filters.
Thanks again Richard for that exc. explanation! I want to get some DSO
filters and your explantion helped a lot.
Chris
-----Original Message-----
From: sf-bay-tac-bounces@No-Spam [mailto:sf-bay-tac-bounces@No-Spam]On
Behalf Of Richard Crisp
Sent: Tuesday, October 11, 2005 9:56 AM
To: The Astronomy Connection
Subject: Re: [TAC] Filter Question
For imaging a narrow filter is appropriate because we can expose a ccd for
an arbitrarily long time.
for visual use a wider filter is better because of the throughput issue you
mentioned.
Hbeta is a good filter for visual because its 486nm wavelength is in the
blue-green part of the spectrum and the eye is sensitive to that. The Halpha
is a poor visual filter because the longer 656nm wavelength is in the deep
red part of the spectrum and the eye just isn't very sensitive to that
wavelength which is why we use red LED lights and red Lucite for covering
out laptop displays.
Ionized hydrogen clouds will emit in the Halpha, Hbeta and Hgamma but the
Hbeta is really the only line that is both relatively strong and a
wavelength that your eye can see readily. The Halpha is actually the
strongest of those lines typically but the eye doesn't see it very well. A
ccd will see from NIR to long UV so it is good at seeing things we cannot
see visually so naturally we may pick different filters for that reason in
that application versus visual.
an [OIII] filter is a good visual one too. I'd recommend the wider ones such
as the Lumicon for visual use.
----- Original Message -----
From: "Chris" <forehaven@No-Spam>
To: "The Astronomy Connection" <sf-bay-tac@No-Spam>
Sent: Tuesday, October 11, 2005 9:50 AM
Subject: [TAC] Filter Question
> Richard, how much light do you loose with each of those filters? (O3,Ha
> and
> S) I've never looked thru any before and have been wondering.
> I've yet to see this aspect of filters discussed in the product
> descriptions
> online. Any reason also why you prefer Ha over Hb?
>
>
> Thanks
> Chris
>
> -----Original Message-----
> From: sf-bay-tac-bounces@No-Spam [mailto:sf-bay-tac-bounces@No-Spam]On
> Behalf Of Richard Crisp
> Sent: Monday, October 10, 2005 10:13 PM
> To: The Astronomy Connection
> Subject: [TAC] Completely reprocessed NGC281 with more exposure time
> added(11hrs)
>
>
> The headline says it all:
>
> http://www.narrowbandimaging.com/ngc281_ap180_cm10_s2hao3_page.htm
>
> have another look if you would.
>
> I may add another two hours to the Sulfur channel and maybe another hour
> or
> two to the Oxygen as well. Halpha seems fine at 2hours.
>
> rdc
>
>
>
Received on Tue Oct 11 14:13:17 2005