FotoDave@aol.com
Mon, 08 Mar 1999 00:30:15 -0500 (EST)
<<In offlist correspondence, Dave has pointed out that advice in my last
message to Joao is wrong as I have confused negatives and positives.
Hi Liam,
Actually, I wasn't pointing that your message was "wrong," honestly. I just
wanted to clarify so that we knew we were talking about the same think.
>> What Dave seems to be saying in his post of 5/3/99 is that the original
camera neg needs a short range in order to fit the straight-line portion of
APH's curve, and suggests 7-8 steps (not stops - this means 7-8 Stouffer
steps, which would equate to 3.5-4 stops, right?)
Yes, and this 7-8 Stouffer steps is the "exposure range." By changing the
first development, one can get different density ranges of reversed negatives
for different processes, but the exposure range is basically the same.
<<
Original (Stouffer) 0.05 0.20 0.35 0.50 0.65 0.80 0.95 1.10
1.25 1.40 1.55
3X/4 sec. flash 0.16 0.21 0.31 0.52 0.79 1.14 1.47 1.78
2.04 2.18 2.30
6X/3 sec. flash 0.14 0.14 0.17 0.20 0.28 0.48 0.77 1.20
1.61 1.96 2.28
>>
I think anyone who is interested in understanding how exposure and flashing
works should plot the chart out. You will see that while both negatives cover
the range from about 0.15 to 2.30, the curves are not the same, but the
straight line section has about the same gamma.
Since the exposure range is low, we are basically choosing which section of
the curve we are using. The low exposure onee give flatter highlights because
the highlights fall on the toe (of the positives). With more exposure, the
highlights go into linear region, but the shadows go into the toe region. Then
the flashing enhance the separation of highlights.
>> The general pattern
for any base/flash combination, in fact, is for separation to be greatest in
the midtones, and least in either shadows or highlights (depending on chosen
factor).
My working method (when falshing is needed) is actually flash to the maximum
(the maximum time that can be exposed without introducing fog). That will give
longest separation possible, and then just use exposure bracketing to
determine which exposure gives the desired separation.
>> In conclusion, I have not managed to improve detail at both ends
simultaneously, though either end can be favoured by an appropriate choice
of exposure factor (low/high for shadows/highlights, respectively). Yet I
do not believe this to be a serious shortcoming of the method because, as I
have said before, a 3X factor produces something that works well for me (or
a 6X factor with pyro-stained originals).
>>
I don't think it is a shortcoming of the method either. If there is any short
coming, it is the characteristic of lith film, which has short exposure range.
But as long as one understands this, there is still a great use for this
method and lith film. For negatives with long scale, we still can try a few
things: the suggested filtration method or the reduction method. Or one can
always use a continous-tone film for long-scale negatives.
Dave S
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