From: Raoul Schlesser (gr842_at_antispamdomain.not)
Date: Tue Nov 25 2003 - 22:34:09 EST
Greg:
(1) you probably already guessed what I'd be saying :)
but:
try a UHC filter... it works!
I had shown a very similar shot a while back as a test image, taken with an EF
200/2.8 II lens, so very similar to your setup. Only difference is that I used an
Astronomik UHC:
http://home.nc.rr.com/rschlesser/Veil_UHC_20031019.jpg
(2) you can enhance your image a bit with processing, as you mentioned. For
example, in Photoshop, try to make a mask that primarily contains the
nebulosity (e.g. copy your image, run it through a median filter to remove the
stars, then use curves to stretch the contrast), then enhance the nebulosity in
your image using adjustment layers with the mask you just made. Of course
there's a number of other, possibly better ways to do this - anything that
discriminates between stars and extended nebulosity will help.
However, it's method (1) that really works and that is more "honest" than (2)
IMHO. Better yet, keep this image, shoot additional filtered images, and blend
filtered and unfiltered - this way you can preserve correct star colors AND
show the Veil clearly.
Hope this may give you a few ideas.
raoul
--- In digital_astro_.at._yahoogroups.com, <gregharp_.at._s...> wrote:
> I'm processing some shots of the Veil Nebula from last night, but I'm having
> some trouble. Basically, while I can bring the levels up to the point where
> I can see the nebulosity, I can't do so without bringing up so many stars
> that it's like viewing it through a snow storm. I'm using ImagesPlus but I
> also have Photoshop CS available, and I'm open to any other tools that can
> help as well.
>
> Here's the relevant data:
>
> Canon 10D DSLR with 70-200mm f/2.8L lens set for 200mm and f/2.8, ISO
1600,
> 30 individual exposures of 60 seconds, no filter (dark skies! woohoo!),
> ambient temperature 32F (0C). The images were converted from raw to 16-
bit
> TIFF and calibrated with a dark frame averaged from twelve originals shot
> shortly after the light frames were taken, a flat frame averaged from five
> originals shot at twilight metered to produce a medium tone (as an
> experiment to compare results to shooting a gray card), and a bias frame
> averaged from five shots at ISO 100 and 1/4000. They were then translated
> and rotated (the latter necessary because I did a poor job of aligning the
> mount) in ImagesPlus.
>
> I've tried stacking these multiple different ways, but I get pretty much the
> same results at different levels. I've done min/max excluded average on all
> 30 frames, I've done adaptive addition of all 30, and I've done simple
> addition on six sets of five frames (producing, effectively, six five minute
> exposures) and then min/max excluded averaged those six images. The
only
> processing I've done on the resulting images so far is digital development,
> and only the values have differed based upon how I combined the images.
So
> far I've just played with the break-point in digital development, and the
> values for the three aforementioned combinations were about 500, 1500,
and
> 3500 for each, basically representing the differences in the signal levels
> I've managed to produce.
>
> Anyway, I can definitely see the nebulosity but there are just too many
> stars to see it clearly. I've seen other shots of the Veil that didn't have
> so many stars in them, and had a much clearer rendition of the nebulosity.
> Is this just fancy processing, like masking the images so that the stars
> don't show up so prominently? If there's more to it than that, what am I
> missing?
>
> Here's a link to a JPEG version of what I have at the moment. This is about
> 1/4 of the original frame, or a 1536x1024 image if you view it at "original"
> resolution.
>
> http://www.pbase.com/image/23629356
>
> Any suggestions?
>
> I'm not sure where I could place a full resolution TIFF of the unprocessed
> version if someone wanted to give it a whack. It's a bit over a 9MB file
> uncompressed, and still about 7MB zipped.
>
> --Greg
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