Re: [APML]: Color Film and Filters

[Jack Schmidling <arf@mc.net>]

Chuck Vaughn wrote:

 
> I'm going to assume some of your post is in jest and you're pulling our
> collective chains a bit...

Not at all.  Just applying a little objective experimentation to prove
what seems intuitively obvious.  I have been wrong before so if you
can convince me that pumpkins are really red, I am all ears. 
 
> Actually all you need is the transmission curve of the filter and the
> response curves of the film in question.


Seems to me it is the eye that we have to reconcile here not the film.
When we talk about proper colors, are we not using the eye as the judge
of what is proper? 
 
> What happened to your new color darkroon? :-)

Like I said, I don't want to be accused of doctoring the process. 
 
> For the benefit of others (because I know Jack knows this) the DS filter will alter the 
>color of stars photographed through it. But it's 
likely to render most nebula just about the same as with no filter. 

>Nebula emit strongly at only a few emmission lines and the DS filter passes those lines 
>with little attenuation. Therefore the DS filter is 
effective at reducing sky fog while not affecting the color of most 
nebula significantly.

Then why do the NA nebula and the Ring photograph red when, with or
without a filter, the eye sees no red, no matter how big a scope one
looks at them with?

Not arguing for the sake of arguing but trying to understand why making
a star red that isn't is cheating but doing the same to a nebula is
somehow advancing the art.

> Here's something I noticed when we were investigating designs for ourH- alpha 
>interference filter...

Just for the record, who is "our"?


>. Interference filters have very high attenuation for
> _about_ 100nm on each side of the design bandpass.

> Above and below they begin to transmit again.

> It appears that the Deep Sky filter takes advantage of this
> characteristic in that high transmission occurs around the H-alpha line.

Interesting if I follow you correctly.

Thanks,

js


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