----- Original Message -----
Sent: Thursday, September 19, 2002 7:38
AM
Subject: RE: [APML] Red / H-alpha work
with film
Hello Tim,
Well, you made me get off of my duff and work on this image. It
is a quick go at it, but I think it may answer some questions. I shot
some short exposures of Cygnus from Spruce Knob with Provia. I then shot
some hydrogen alpha (Lumicon) through the Pentax 105 at f4 from a moderately
light polluted location on E200. BTW, I did push process the E200 two
stops and the grain is pretty noticeable. I thought I would then use the
hydrogen to enhance the reds in the Provia. I shot for one hour (details
on website) on the E200 thru the filter. I did have some significant
light pollution gradients. I had to correct for this and that altered
the star brightness and thus the red color balance of the stars. I then
mixed the hydrogen alpha with the red channel from the Provia to try and
maintain the star color balance in the gradient corrected areas.
That
is one question I have, how to do a color gradient correction in an area
without altering the star color balance? Any help would be greatly
appreciated.
Here
are the links:
The
HydrogenRGB
The
halpha with gradient correction. You can see the star brightness
difference in the upper right.
I
don't have time to post the straight RGB with the Provia. I think you
can do some good work with the hydrogen alpha from a light polluted
environment. Especially if you are going to keep it in black and
white. The gradient corrections are less noticeable compared to when you
try to assign color to the areas. Best wishes and keep us posted.
Nice pictures you posted recently!
Jeff
Ball
The inspiration for this "idea" is from Robert
Reeves most excellent book
WIde Field Astrophotography as well as some of
the H-Alpha pictures
the CCDers are posting. I was thinking of
using a red filter in my mag 3.x
skies and shooting say M42. I don't want
to deal with TP and hypering
etc so was wondering if E200 would be a
reasonable film. Scan the
image and take only the red channel, then
convert this to B&W. I hink
you would end up with a decent looking B&W
which one can do from the
backyard.
I'm guessing a true H-alpha filter would have
way to much a filter
factor to consider film?
Thanks for any comments,
Tim Povlick
San Juan Capistrano, CA