Re: I like toes and shoulders

----- Original Message -----
From: "Shannon Stoney" <sstoney@pdq.net>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, September 29, 2005 1:03 PM
Subject: I like toes and shoulders

> >
>>Film has a limited exposure range. Traditional B&W
>>negative films can
>>record 4 to maybe 5 stops on the linear portion of their
>>H&D curve. Below
>>that is the non-linear "toe" region, which has a lower log
>>D per log
>>exposure slope than the linear portion and therefore
>>compresses the scene
>>luminances (shadows) that fall there. Above the linear
>>portion is the
>>"shoulder" region, where the slope is again lower than the
>>linear portion,
>>which compresses high-luminance values (highlights) that
>>fall there. Since
>>the average daylight scene has 10-14 stops of luminance
>>variation, it is
>>clear that you cannot fit all of the scene luminance
>>values onto the linear
>>portion of the curve.
>>
>>By using "minus" development, one can squeeze more scene
>>luminance values
>>into the linear portion of the curve, at the expense of
>>overall lower
>>contrast (i.e., less separation of tonal values in the
>>linear portion, and
>>very low separation in the toe and shoulder regions).
>>Also, modern films
>>(in particular, T-Max) have longer linear portions. In
>>fact, it is hard to
>>find the shoulder with TMX and TMY -- density just keeps
>>climbing. So:
>>Given a modern, long-density-scale film [NOT necessarily
>>long-EXPOSURE-scale], and a suitable low-contrast printing
>>process, the
>>answer to this question is a qualified No, it doesn't
>>matter much -- you
>>can slide things up and down the curve (within reason)
>>with little effect
>>other than printing time. However, with traditional films
>>(and
>>particularly with HP5+), you do need to be careful where
>>you place things
>>because these films do not have excess headroom.
>
>
> For some reason prints from TMX and TMY negatives look
> funny to me. They look sort of...too perfect or modern or
> something. Maybe this is because of the absence of toe
> and shoulder characteristics you are talking about. I
> have resisted switching to them because of the "look." I
> wonder if I have just become habituated to seeing older
> prints as the standard, so prints made from newer films
> look weird. I wonder if anybody else has this problem?
> Can we outgrow it? Should we?
>
> I remember going to a show of landscape photographs here
> in Houston. They were lovely, but they had this quality of
> being sort of too thin-looking or something. IT's hard to
> describe. I thought, "I bet that's T-max," and then found
> out it was. On the other hand, I saw some of George
> Tice's photographs and they looked "right" to me, and I
> think he told me that he used Tri-X. He photographs at
> dusk a lot, and so there are a lot of areas that fall in
> the toe. But it seems strange that "right" should mean
> "poor separation"! Maybe i need to get over this.
>
> --shannon
>
>
   There are two Tri-X films, both are available as roll
films, only one (ISO-320) in sheets. The ISO-320 stuff has a
very long toe curve. Actually, the curve is upward deflected
along its whole length. This does result in a difference in
the tonal rendition compared to a film with mostly a
straight line characteristic like T-Max 100 and 400.
Traditionally, "portrait" films have had curves like Tri-X
320. AFAIK, it is the only one of this sort left. Because of
its peculiar, all toe, curve increasing exposure beyond a
certain minimum will not change its rendition much. That is,
increasing exposure will not push the exposure up the curve
to the straight line portion because there is no straight
line portion, however, overall contrast index will increase.
  For films with "normal" shapes There is a certain minimum
exposure above which there is little or no change in tone
rendition over a range of many stops. Loyd Jones determined
that this was the exosure that placed the darkest parts of
the scene of interest at the point where the toe contrast
was about 1/3rd of overall average contrast. His tests,
which included a very large double blind survey of many
prints showed that there was no preference once the negative
had been given enough exposure to make the "first excellent
print". Prints made from negatives given more exposure were
judged equal to this over a range of around 10 stops. This
was done in the late 1930's or mid 1940's when film had less
latitude than it does now. Negatives given the minimum
exposure for an "excellent" print did have the advantage
that both grain and loss of sharpness from internal
scattering of light in the emulsion tend to increase with
density. So, especially for small format negatiges, there is
an advantage in having the thinnest negatives consistent
with good tone rendition. Jones based his speed system on
these results. This system was used internally by Kodak
beginning about 1940 and was adopted by the ASA, with some
changes, in 1943. Unfortunately, one of the changes was to
include a 2.5X safety factor which resulted in overly dense
negatives. About 1958 the ASA changed to the DIN system of
speed measurement (which was easier to to in practice and
made no significant difference in toe speed) and at the same
time dropped the safety factor, essentially doubling the
speeds of all films on the market.

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