----- Original Message -----
Sent: Friday, December 20, 2002 11:56
AM
Subject: Re: [APML] some ideas
Hello,
Since I am now mired down in
a confirmed El Nino winter (storms go from Japan all the way to CA) and the
only good prospect is awesome skiing, here's a few thoughts that might or
might not work for chrome users...
First off, chrome is more
contrasty than negative film... it's possible to get the bright parts of
anything to show up and have the rest of the image fade into black. Pushing
chrome films by developing them longer in the first developer does two
things... it opens up the shadow areas and it converts any blue caste in the
shadows to a more neutral gray. Not all films have the "blue shadow" problem
but if they do, this cleans them up. If you leave the film in for more than
2 stops the Dmax begins to disappear, this is actually a good thing for
astro stuff because when you scan a chrome, pure black = no data. You never
want to use chrome film that has a pure black... you can always set the end
points AFTER the scan... but if you have to scan pure black, you ain't got
nuttin', honey.
The other major
problem with chrome films is the bright stars... if exposing to sky fog or
pushing to sky fog, the bright stars go ballistic. What to do? I have not
tried this yet but I think it will work...
1. Shoot a
series of shorter exposures that have the stars as smaller points and have
color.
2. Here's
the laborious part.... put a circular selection around the short exposure
star that looks the best from the "short exposure series" and cut and paste
it on top of the blown out star. This will now be a layer sitting on top of
the blown out star. Go to your layer control box and see how much you need
to reduce the opacity of the top layer until the dark ring surrounding the
star blends into the blown out part of the star below it. This will give you
some idea for the next step... go back to 100% and take the eraser tool at
10% and start to whittle away at the dark ring... you will hit a point where
the remnant of the "dark ring" blends in perfectly with the surrounding
areas below it.. If there are any color issues, you can adjust the top layer
to match the bottom layer. Theoretically, you can replace your worst stars
with nice ones using this technique. It is not complicated but it is a bit
laborious... just the thing for those days of being house bound as winter
blizzards howl outside and the snow piles up over the observatory...
Tony