Re: AW: [APML] Tenerife skies (was: Exposure times with IDAS filter)

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

Hi Glenn:
Are you saying that the skies are terrible there right now (from Sahara
dust) and for the forseeable future? In other words, when did you make your
measurements and how far into the future can you extrapolate? Or is this a
daily measurement? Ulrich is talking about going in April.
Thanks....
Bert

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


----- Original Message -----
From: "Glenn Shaw" <gshaw@alaska.net>
To: <astro-photo@seds.org>
Sent: Sunday, January 06, 2002 1:59 PM
Subject: Re: AW: [APML] Exposure times with IDAS filter


Tenerife has pretty terrible skies due to extensive, thick dust blowing from
the
Sahara Desert. I made optical depth measuremetns there, finding the optical
depth at 500 nm wavelength to be between 0.15 and 0.25. You would be much
better
off staying completely away from northern Africa and going to the southwest
US,
Australia or Hawaiian Islands.

glenn shaw

Ulrich Beinert wrote:

> Matt,
>
> thanks for the tips. Even if the skies are not 7m, they'll be way better
> than anything I've ever had in my life. Europe is a really unfortunate
place
> to be if you're an astrophotographer (or doing any form of astronomy for
> that matter). It's just too crowded here! :-)
>
> When you were on Tenerife, were you up on the mountain? How good were the
> skies? Do you have any pictures from when you were there? There are some
on
> this website: http://aida.astroinfo.org/levens/
>
> Ulrich
>
> -----Ursprüngliche Nachricht-----
> Von: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]Im
> Auftrag von Matt BenDaniel
> Gesendet: Sonntag, 6. Januar 2002 15:29
> An: astro-photo@seds.org
> Betreff: Re: [APML] Exposure times with IDAS filter
>
> Ulrich,
>
> I've been to Tenerife and the skies are definitely not as dark as mag 7.0.
> One possible problem they have is sometimes they get fine Saharan dust in
> the air, which can ruin the transparency. I would say don't use the filter
> if the transparency is good. Also, I would only use the filter for
emission
> nebulae. The rule of thumb I use is 1.5x exposure time with the filter.
>
> Matt
>
> At 11:35 AM 1/6/2002 +0100, Ulrich Beinert wrote:
> >When using my IDAS filter from my "dark-sky" site, which has a lim. mag.
of
> >about 5.5, I can expose twice as long when using the IDAS filter in order
> to
> >get the same background brightness.
> >
> >In April, I'll be flying to Tenerifa, where the sky will be *very* dark
at
> >2200m altitude. Still, I'm thinking of using the filter anyway, because
> >there will always be *some* light pollution, and I've heard that using
the
> >filter at 6.5-7m sites makes sense too. Can I also double the exposure at
> >such a dark site, or would that cause the background to get too bright?
> >
> >Ulrich
>
> --
> Matt BenDaniel
> http://starmatt.com
>
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