Re: [APML] Bill Fletcher's Tri-color work(was 23a filter)

[Chuck Vaughn <aa6g@aa6g.org>]

Michael,

>       Actually, hypered Tech Pan is very slow film when compared to Kodak PPF.
> It is especially slow in green light and you may loose some of the ionized
> oxygen spectrum if the green filter does not cover the region.  My original
> tricolor image of Antares-Rho Ophiuchus in 1993 took a combined exposure of just
> under 4 hours at f/2.5.  In comparison a set of 2 PPF exposures at f/2.5 would
> take less than one hour total.

I have a different experience and opinion here. It could be that my blue and
and green filters have higher transmission than what you used. Were your's a
#47 and #58? If so mine do have much higher overall transmission. Also I don't
know if in 1993 that anyone was high vacuum hypering TP to 0.6D like it needs
to be for maximum speed. These things combined probably explain what I've
noted in the following paragraph.

Currently my exposure limit in white light is about 120 to 135 minutes at f8
from Chews Ridge. With the red filter I get a very well exposured negative
in 180 minutes. The blue and green exposures really need to be 360 minutes,
but that's another story. F2.5 is 10.25 times faster than f8. That makes the
previous numbers for TP at f2.5 12-13 minutes in white light, 18 minutes in
red and 35 minutes in green and blue. That's faster in white light and only
a little longer to take a tricolor compared to two 30 minute PPF exposures. 

It's also becoing clearer that with the work that Philip and others are
doing with longer (and multiple) exposures on color film to get images that
are approaching what you can get with TP that with all considered color
film isn't that fast or TP that slow after all.

Chuck <aa6g@aa6g.org>

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