Re: [APML] Film Color Response

["John Boudreau" <jeboud@mediaone.net>]

Hi Bill,

The problem is that the emission nebula reds occur the hydrogen-alpha line
at 656nm, and that the newer Fuji "4th layer" color negative film almost
completely miss this emission line. Just a few years ago many films from
Fuji and Kodak had their red sensitive layer peak around 650nm, and the peak
was fairly broad and covered emission nebula reds well.

Designed to record "less pink" in flesh tones, the current Fuji "4th layer"
and Kodak Portra film red layers peak around 620 to 630nm, and the
sensitivity curve of this layer drops very suddenly by the time it crosses
656nm (except Portra800-- it's still peaks around 650nm). That's why these
films miss emission nebula reds. Fuji's "4th layer" itself has nothing to do
with this--- the 4th color layer is meant to record greens better and give
better color balance under artificial lighting.

The new Fuji negative films still work well for galaxies, meteors, and
auroras. Except for missing the emission nebula reds in galaxies, the other
reds in the night sky can record well. For instance, aurora reds occur at
630nm, still in the sweet spot of these new films.

John Boudreau
jeboud@mediaone.net
http://people.ne.mediaone.net/jeboud/astro.htm

----- Original Message -----
From: William R. Mattil <wrmattil@ix.netcom.com>
To: <astro-photo@seds.org>
Sent: Tuesday, January 22, 2002 8:35 PM
Subject: [APML] Film Color Response


> Hello,
>
> I just recieved back some pictures that I took from my last dark-sky
> trip and ran into something that makes me a bit curious. On two
> consecutive nights I shot some piggyback pictures of up to 1 hour
> duration. First night I used Kodak Royal Gold 100 ASA and the second
> night I used some Fuji Superia REALA 100 ASA with the same exposures.
> The differences between these two films are startling. The Kodak shows
> good red response (M42 appe ars red as does the flame and horsehead. The
> Fuji shows no red nebulosity at all. M42 is green, Flame and Horsehead
> are not visible at all. But Betelgeuse is red.... curious. Is this
> normal for this film ? (the fuji). The archives seemed to indicate that
> it wasn't a bad film. I also have a few dozen rolls of Fuji Superia 800
> ASA that I am afraid to use now because of this. I seem to recall that
> Fuji may have changed their emulsions (4th layer technology ?) and this
> wasn't good for Astro work. Can anyone fill in blanks here ?
>
> Thanks !
>
> Bill
> --
> William R. Mattil | Fred Astaire wasn't so great.
> wrmattil@ix.netcom.com | Ginger had to do it all backwards
> (972) 399-4106 | and... in high heels.
>
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