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Re: [APML] Bill Fletcher's Tri-color work(was 23a filter)
Brian and Leau Larmay wrote:
> You know, I brought up the same topic once about tri- color vs. your average
> color astro film on the deja astronomy NG and got knocked around as to the
> method being to much work and not worth it.
>
> Personally I dont get why its any harder, in fact, I want to try it once to
> see what it is like also.
> Tech Pan...thats a really fast film right?
> How fast is fast?
> Would the standard red, green, blue filters work by Cokin, or do they have
> to be a certain kind of RGB filters?
>
> Brian
>
> ----- Original Message -----
> From: Ulrich Beinert <analemma@gmx.de>
> To: <astro-photo@seds.org>
> Sent: Thursday, June 15, 2000 6:28 AM
> Subject: Re: [APML] Bill Fletcher's Tri-color work(was 23a filter)
>
> >
> > > Hello Scott:
> > > We all owe a lot to Bill Fletcher. He was a pioneer in
> > > film-digital astrophotography (not just tricolor). I believe he
> > > perfected his process in 1992 or perhaps 1993, which was years before
> > > anyone on this list was doing such work. He did this with Photoshop 2.5
> > > (no layers) which made it vastly more difficult than it is today. He
> > > spoke to Adobe and they thought his process at the time was impossible.
> > > Even with this discouragement he was able to develop a process that
> works
> > > quite well. In the November, 1994 Sky and Telescope on page 98 he wrote
> > > an article on his technique. The article was general and gave little
> > > specific data. The lead photo of the article was a tricolor of
> > > Antares-Rho Ophiuchus region which I took with my Tamron 180 mm f/2.5
> > > lens and hypered Tech Pan film and Bill processed in Photoshop 2.5. It
> > > has been a long time since I took that photo (I think it was in 1993).
> I
> > > believe I used a Kodak 25A for the red, 58 for the green and 47 for the
> > > blue. The exposure times were 42 minutes in red, 80 minutes in green
> and
> > > 100 minutes in blue. In later work I increased the green and the blue
> > > exposures. In my experience the hypered Tech Pan is least sensitive to
> > > green light. The most challenging tricolor I have done was of the very
> > > dim SNR Simeis-147.
> >
> >
> > If I understand this right, you take one photo through a red filter, one
> > through green, and another through blue? Then what - stack them in
> Photoshop
> > assigning them to the red, green and blue channels, respectively, to get a
> > color image? This sounds interesting; I want to try it....
> >
> > Ulrich
> >
> >
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> >
>
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Hello Brian:
Actually, hypered Tech Pan is very slow film when compared to Kodak PPF.
It is especially slow in green light and you may loose some of the ionized
oxygen spectrum if the green filter does not cover the region. My original
tricolor image of Antares-Rho Ophiuchus in 1993 took a combined exposure of just
under 4 hours at f/2.5. In comparison a set of 2 PPF exposures at f/2.5 would
take less than one hour total. The main advantage for the tricolor is that Tech
Pan is a far better film than any of the color films past or present. My PPF
photos had colors very close to the tricolors of David Malin.
--
Michael Stecker
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