[pure-silver] Re: Suggestions needed from the real experts here
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 22 Jun 2006 21:01:44 -0700
----- Original Message -----
From: "Mark Blackwell" <markb1958@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, June 22, 2006 7:39 PM
Subject: [pure-silver] Re: Suggestions needed from the real
experts here
prints.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
Thanks for the help Richard. Next time I might just
develop normally and test that out too. In fact sometime
soon I might do it on purpose to see what happens I am
sure it won't be the last time the dummy behind the
viewfinder makes a mistake. LOL A drop in contrast might
actually help this particular subject, but a higher
contrast paper is an option if needed. I ended up using
recommended development time x .80 for the Tri X and x .90
for a role of T Max that was also done the same way per
kodak recommendation. Even if it was bad advise, its
worth knowing that too.
One thing I will say that I was a bit surprised at these
days. First the Kodak site had a phone number to call
with a question. Second someone answered the phone
promptly, politely and answered my question. No long
waits. Only one or two menu items to get to a person. I
like a lot of different bw films, but I am going to buy a
lot more Kodak because of the fact that they took my call
and answered a question.
For some reason I forgot about Kodak's customer service,
its among the few left where the people actually know
something about the product. In the USA the number is 1 800
242 2424, professional photo products are at extension 19.
If you cut back development by only 10 or 15 percent you
will get about normal contrast negatives which will be
rather dense. They should print well. Depending on the
subject some overexposure is sometimes benificial.
C.1940 a group at Kodak Research Labs, led by Loyd A.
Jones, conducted very extensive research into the tone
rendition of film and paper. Jones had been working since
the 1920's (perhaps even before) on means of measuring film
speed that would have some significance to the practicing
photographer. Earlier methods were of interst to emulsion
researchers but of limited practical application to
pictorial photography. Jones's method was eventualy adopted
by Kodak as its standard internal method and "Kodak" speeds
began to be published c.1940. A modification of this sytem
was adoped C. 1943 as the orignal ASA system.
In their research into tone rendition and film speed
Jones's object was to find the minimum exposure which would
yield an "excellent" print. The reason for minimizing the
exposure was because films of the time became grainier and
lost some sharpness with density. This is still true but not
to such an extent. It was thought that the thinest negative
which would yield "excellent" tone rendition was the
optimum. What Jones found was that after a certain minimum
exposure was reached the tone rendition did not change for
increased exposure over a very wide range. So, while minimum
exposure has some benifit in minimizing grain and maximizing
sharpness it does not have much effect on tone rendition
provided that the exposure is enough.
The criteria Jones settled on for his speed method was to
set the minimum density which was to have any detail at a
point on the toe where the gradient was 0.33 of the straight
line portion. In practice, this proved very difficult to
measure, so when the ASA revised the speed method in 1958,
they adopted a method used by the Germans. This DIN standard
was not the one from the 1930's but a newer method. The
speed point was defined as a fixed density above gross fog
and support density when the film was given a standard
series of exposures and developed to a specified contrast.
The ASA in testing this method found that the difference
between speeds given by it and by the Jones minimum gradient
method were very close provided a correction factor was
applied to move the speed point up the toe. The ASA found
after surveying a large number of films on the market at the
time that if the speed from the DIN method was corrected by
multiplying by 0.8 it would agree in nearly all cases with
the Jones method. In addition, the original ASA speed
standard for some reason included a 2x safety factor. This
turned out to be a blunder since most exposure errors are in
the direction of over rather than under exposure, so when
one used the ASA speed one got rather dense negatives. When
the new method was adopted in 1958 the fudge factor was
dropped and all films doubled in speed overnight.
The point of this is to show that overexposure by 2 or
even more stops does not wreck the tone rendition of the
resulting print. It may take longer to expose but the
results will be the same.
As far as minimum exposure goes, its of some value for
small format negatives, mainly 35mm. By the time one gets to
2-1/4 x 2-1/4 there is probably little gain and none for
larger sizes.
For underexposure you are generally cooked. Since the
film speed gives about the minimum exposure that will yield
good tone rendition any further reduction is likely to
result in empty shadows or distorted mid grays if contrast
is increased in an attempt to make the shadows look right.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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