Re: [APML]: Color Film and Filters

[Chuck Vaughn <aa6g@aa6g.org>]

Jack Schmidling wrote:
> 
> The original objection I had was making stars that are not red, red and
> I guess we agree that this in not legit because stars are stars.  If
> a filter does this, to a color photograph, it presents an untrue
> image even if it brings out other reds that really are there but can
> not be seen.

The main idea of the DS filter is to allow more nebula to be recorded.
You just have to ignore the fact that star colors will be altered and
enjoy the nebula. :-)

> The other detail is a question:  Just what color is the sky?

If you went to a site where manmade light pollution was completely absent
(and no auroras), I think the sky should be green as that's the color of 
the natural airglow. With manmade lights around I would think it could
vary depending upon the type of lights that predominated.

There's a few other things that probably affect how color film acts during
a long exposure. Does each layer gain exactly the same speed during 
hypering? And same fog level? Does reciprocity failure affect each layer
exactly the same over varying times? I don't have the answers to these
questions. 

Considering the variance I've seen among the various films used for color
astrophotgraphy, I suspect the response of the layers is different for
different films. H-alpha is definitely *red*. Yet I've seen the same nebula
with varying degrees of red on different films.

I don't think anyone using color films for astrophotography is claiming
their photos are _true_ representations of the universe nor do I think
they should worry about it. I prefer to think of them as approximations
and enjoy them for what they are.

Chuck  <aa6g@aa6g.org>