Re: AW: [APML] Exposure times with IDAS filter

[Glenn Shaw <gshaw@alaska.net>]

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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