The principle of the Zone system gives a good illustration of how to
get
B&W film to record the maximum tonal range, although in practice it can
be
time consuming to get the 'best'. In this case one can use incident or
just
put the camera on 'A' or 'P' and trust to luck!
This is probably 'old hat' but I followed a technique in a book (I
can't
remember off hand which one though - I've lent it to my son), to
determine the best exposure index (EI) and development time for a given
film/developer combo for 35mm film.....
I set up a still life subject with white and black knitted woolen
jumpers, a
chequered grey shirt and some textured building bricks (although any
subject with full tonal range could be used). The lighting was bright
northern sky. The exposure starting point was an incident reading which
was compared to a spot from the high, mid and low tones at ISO 125.
The procedure was to expose a sequence of frames of the subject at 1/2
stop increments to cover about 6 stops. The strip of film was removed
from the camera and processed as recommended. The exposure sequence was
repeated using the next section of film in the cassette, removed and
processed for +10%. A third sequence was exposed and processed at -10%.
The negatives were examined and by assessing which negatives had the
most detail in highlight, mid tone and shadow areas, suitable
combinations of speed index and development were determined. This can
then be refined by using finer variations of speed index and
development
times. From memory, Ilford FP4 exposed at EI 80 and developed for
standard time in Ilfosol S gave me the best results.
I have found that with that combination, an incident reading puts tones
equally on the curve. However, really bright highlights and deep
shadows
will not register.
This then should be done for each camera/film/developer combination.
The
trouble is, there's no time to go out and take photographs.......!
Factors such as shutter speed accuracy and temperature control all have
a bearing etc.etc...
John
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