Re: [APML] My first Tricolor Shot

[Chuck Vaughn <aa6g@aa6g.org>]

Volker,

> A friend of mine was doing this, but I have to tell you that it was not
> that exact way, you did it! His results are 1:1,7:2 for my filter set.

Did he obtain the results from calculations of the filter responses in
combination with TP response or did he perform photographic tests? I
found that calculations for my green filter closely matched the photographic
test but the calculations for the blue filter showed that it would require
less exposure than the photographic test indicated was needed.
 
> O.k., thatīs what I did this morning. Please take a look at
> http://www.spiegelteam.de/NewPictures.htm . Iīve added a new version of the
> image. I made NO (!) color correction. If you look at the color information,
> you can see, that the background is a little bit uneven, but the average is
> roughly equal.

I've found that's the best you can do. The sky background and the level
settings look *much* better.
 
> First thing I did was setting the background of the bw-images to the same
> level. Thatīs what I forgot to do in my first version. For my "taste", the
> image is a little bit too green. How can I correct this for future? By
> reducing the exposure time for green? Or would you lower the green contrast?

It doesn't look green on my Sony monitor. From other galaxy photos I've
seen it looks like there may not be enough blue.
 
> I have a new result now, but are these colors roughly correct?

It's very hard to say just what "correct" is.

>I think that
> one should take an image of a G-Star as our sun. Did you do such a test?

No, I didn't do that. If you go to my articles page:

http://www.aa6g.org/Astronomy/articles.html

and look at "Assembling a Tricolor Astrophoto" you'll see I photographed a
Kodak grayscale by moonlight.

I probably asked this question before but if you have a link to the
curves of your filters I'd like to see it again. My experience with my
tricolor photos and looking at David Malin's is that nebulas in external
galaxies come out white or very pale pink. Strong red usually indicates
low OIII response at 500nm.

Chuck


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