Re: Only shades of gray...

----- Original Message -----
From: "Tom Ferguson" <tomf2468@pipeline.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, June 08, 2004 8:00 PM
Subject: Re: Only shades of gray...

> I keep wanting to reply to this thread, but can't remember
or find the
> original source I'm thinking of.
>
> One of my original teachers was Fred Picker. A very
opinionated and
> original photographer / thinker / teacher. One of his
assignments was
> to print as many distinguishable "shades of gray" as
possible on a good
> silver gelatin paper. His intention was to teach "what
were worthwhile
> and what were homely shades of gray" (paraphrased) . I
think he claimed
> "about" 80 or 100, I really can't remember what I printed.
I remember
> thinking (much latter) that Adobe's 8 bit (126 shades)
seemed more than
> enough.
>
  I sent a long reply to this but failed to make an
important point, to wit, for all practical purposes the gray
scale of the paper is continuous so there are really no
steps. The overall scale varies from the paper's maximum
black to the white of the emulsion backing. For reflection
prints the maximum white depends on the level of
illumination. Paper white is probably around 90%
reflectivity for Baryta or RC white papers. Dmax of most
emulsions is never used despite all the controversy about
which paper or developer yields the maximum black. In a
reflection print it is difficult to perceive the difference
between, say, log density 1.8 and log 2.2. If the paper is
textured or has a matt surface the range is reduced on both
ends. This is really a measure of the _visual_ contrast the
paper is capable of, in distinction to its photographic
contrast which is a measure of the difference in exposure
needed to produce a fixed degree of variation of density.
   Since the paper gradation is continuous the perceived
separation of tones depends on the visual system and the
things which affect it, like illumination level. There is
really no such thing as a minimum difference in tone, at
least in relation to anything practical in making good
prints.
   In theory the tone reproduction is probably not really
continuous because of the effect of grain but in practice it
is nearly enough so to consider it to be for visual
purposes.
   One might ask how small a difference in gradation in the
negative will be reproduced. I think the answer to this is
that, for all practical purposes, the paper will reproduce
the smallest variation the film is capable of.
   Some aspects of tonal reproduction seem to be perpetually
confusing and the voodoo language used by some writers does
not help. One of the most prolific researchers into tone
reproduction was Loyd A. Jones, of Kodak Research
Laboratories. Jones wrote a great many papers. Some were
published in the _Journal of the Franklin Institute_ and
some in other journals. I think several were in the _Journal
of the SMPTE_ and elswhere. They are worth reading. Jones
was concerned with the making of "excellent" prints. He
researched the proper method of measuring film speed so that
it bore some practical relationship to good prints. He
extensively researched the range of brightnesses to be found
in actual scenes and what film characteristics would lead to
good reproduction of them. It is too bad that the man and
his work have fallen into relative obscurity.

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