This is a toughy. There is a visible difference between most pan
films and T-Max, which has relatively flatter color response, i.e.,
less blue in comparison to other colors. Technical Pan has both
increased red sensitivity and somewhat extended red sensitivity, that
is, sensitive further toward I.R. This results in a peculiar rendition
of skin, not exactly washed out but sort of transparent looking. I can
be flattering for some people. I find T-Max looks like other films
when they are used with a No.8 (old K-2) filter. That is skys are a
bit darker and clouds more contrasty.  Most of the variation in other
pan films is in the green region. The older senstiizing dyes tend to
produce a dip in response in the greens. This is less pronounced or
gone in some more modern pan films, for instance T-Max. In general, I
find that the overall curve shape has much more effect than spectral
response. Filters will swamp out the film spectral response. You
really have to make comparison tests of the same subject matter to see
the effects of the film, it can be quite subtle. I have gotten to I
can judge the tonal rendition of color in B&W to some extent but not
enough to predict what a particular film will look like.

Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

Astronomers do all the time. Many interesting objects
shine in just a couple of wavelengths, and sensitivity
to the hydrogen alpha line (656 nm, red) or the oxygen
III line (500 nm, blue-green) is crucial.

Few black and white films have any useful sensitivity
to the hydrogen alpha line. Technical Pan is an exception.

Colour films make this even more complicated, since
the oxygen line falls right between the sensitivity
of the blue- and green-sensitive emulsion layers.
So emission nebulae are greenish-grey to our eyes
(which are most sensitive to green), but photograph as
pink, because the film is more sensitive to red than
to this particular shade of green...

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89mg                    pied a terre..."
ICBM: 49 16.05 N 122 56.92 W       - Hospital/Shafte

I looked at the Ilford website just to be sure about the response of PanF+.
The response is generally pretty flat, but it falls off severely in the
violet and significantly in the far red, and so do your eyes - the film is
actually much flatter than the photopic response.  A No. 8 filter would
probably make scenes look pretty normal.  Ilford doesn't give much guidance
about filters, but, since the response is pretty normal for a panchromatic
filter, you can assume a filter factor of 2 for a start.  If you need to
bring up the red response, a CC30R looks about right (or you can use an
orange or red filter if you want to cut the blue more).  The falloff in the
violet is usually an advantage for outdoor work, since it reduces haze.  If
you don't like it, a CC50B or maybe an 80A filter would probably even things
out.  Of course, filters absorb light, and will reduce the already low
effective exposure index.