Re: [APML] Bill Fletcher's Tri-color work(was 23a filter)

["Ulrich Beinert" <analemma@gmx.de>]

> 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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