Re: [APML]: Color Film and Filters

[Steve Bell <sb635@delphi.com>]

Jerry Lodriguss wrote:
> 
> 
> I dont' know why everyone is saying that the deep-sky filter is a red
> filter.  Mine is distinctly blue-green when held up to the eye.  Now, mine
> is about 12 years old, so maybe the new ones are red.  The OIII filter is a
> red filter visually, maybe people are confusing that one.

If your DS looks blue-green, then it is definitely different than mine. I don't know 
if this is a valid comparison, but if you look in an Orion catalog, they show a 
picture of their SkyGlow filter (which has a very similar transmission curve to 
Lumicon's DS) and it looks purple-red, just like my DS. That's why I've always 
considered my DS to be a "red" filter. But I haven't done any color work, and I 
certainly accept what you and Chuck have said - good color work can be done through a 
DS (or a SkyGlow, I imagine). This is actually great news for me, living in a big 
city.

> 
> As Chuck has already noted, most of the stars get overexposed and turn
> white. I see a LOT of stars on the deep-sky fitler pix with red halos around
> them. I have had this problem for a number of years with the Fuji films on
> red stars and I always attributed it to light spreading in the red layer, or
> halation off the film base since the red layer is next to the base.

Yes, I noticed the slight halation on the photos on your page. I am very glad to see 
that stars on color film through a DS turn out mostly white.

> 
> Here are the two things I'll throw out for speculation.  One is that my
> filter is 12 years old, and possibly the band pass has shifted, and yellow
> light is getting through.

I think I have read that interference filters like the DS somehow absorb moisture over 
time, and perhaps this has occurred with yours. I don't know, but I wouldn't imagine 
that that would actually cause it to appear to be a different color to the eye, 
though. If your DS looks blue-green, Lumicon must've done something to its design 
between 12 yrs. ago and the present. I wouldn't discard your older DS, though - you 
probaly have the only one that can pass near-yellow frequencies!

> 
> The other is that there is something emitting in the orange region of the
> spectrum in the Veil, and it is simply overexposed on the negative and
> appears more yellow than orange.
> 

I also thought something similar - could it be that after hypering, this new PPF-2 
film undergoes a slight color shift and shows yellow for things that are actually more 
orange?

I'm psyched!! I'm almost convinced to go out and buy some of this new-fangled color 
film!

-- 
Clear skies,
Steve Bell
sb635@delphi.com
http://people.delphi.com/sb635 - Astrophoto page