[alt-photo] Re: Multi-Neg Printing Methods

[etienne garbaux]

>I seriously doubt that you could possibly produce more tones from 
>seperation negs than are in the original 
>shot.   *   *   *    doesn't platinum yield a huge tonal range anyway??

Sorry to pick on this post, and I sincerely intend no personal 
affront -- but it is a good example of the confusion that can be 
caused by talking casually of "tones" instead of being precise about 
what is meant.

What is meant by "produc[ing] more tones from separation negatives 
than are in the original shot"?  What are the "tones" that are 
produced from separation negatives?  Print densities?  (If so, please 
say "print densities" rather than the ambiguous "tones.")  What are 
the "tones" that are "in the original shot"?  Scene 
luminances?  Negative densities?  Print densities?

The original scene almost certainly has more "tones" -- i.e., greater 
tonal range, or range of luminances -- than any negative, or any 
printing process, can reproduce.  If it is an outdoor scene in 
daylight under a clear sky, the luminance range will be on the order 
of 1,000,000 to 1 (a range of 6 in density units), or even more in 
direct sun.  Negatives for printing with iron or plain salt processes 
will generally have a density range ("DR") of 2 to 2.7, or from 100:1 
to 500:1 -- more than 1,000 times less than the original scene.  And 
finally, a full-range Pt print may have a DR of 1.4 to 1.6, or from 
25:1 to 40:1 -- at best, 25,000 times less than the original 
scene.  A full-range silver-gelatin print will have a DR of around 2, 
or 100:1.  Indoor studio scenes with carefully controlled lighting, 
or drab outdoor scenes under heavily overcast skies, may have scene 
luminance ranges as low as 1,000:1 (3, expressed in density units) -- 
still 100 to 400 times greater than the range that a print can reproduce.

Any properly calibrated process should allow one easily to produce 
the full range of print values, whether that is 25:1 (Pt print on 
buff paper), 40:1 (Pt print on bright white paper), or 100:1 
(silver-gelatin print on bright white paper).  (And note that Pt does 
not, in fact, have a "huge tonal range."  The "tonal range" of a 
print is its density range ("DR") -- and the DR of a Pt print is at 
best less than half of the DR of a good silver-gelatin print.  Pt 
does have a large exposure scale ("ES"), but that just means it needs 
a negative with a high DR to produce the full range of print 
densities or "tones" -- it says nothing about the range of densities 
or "tones" in the final print.)

The difference between workflows is in WHICH scene luminances 
("tones") end up matched to WHICH print densities ("tones").  It's 
all in the mapping.  Digital imaging "curves" are one powerful means 
to adjust this mapping.  Multi-negative printing is another.  + and - 
exposure and + and - processing are less flexible methods.

There is no magic to all this.  Just start with the printing 
process.  Find its ES (the range of exposure required to get from 
Dmax to Dmin).  This is the DR necessary for a negative that produces 
the full range of print densities.  Now, figure out what you need to 
do to get the various scene luminances to produce the particular 
negative densities that you need to give you the print densities you 
would like mapped to each possible scene luminance.  The only way to 
do this is to test, test, test.

You will need to do this individually for all of the scene luminance 
ranges you normally encounter, then use the process that matches the 
actual scene luminance range.  (Since in-camera exposure is the first 
control, you need to decide on and commit to the process you will use 
before you expose the film.)

Best regards,

etienne