[pure-silver] Re: Contrast grades
- From: "BOB KISS" <bobkiss@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 27 Jul 2013 18:23:17 -0400
DEAR RICHARD,
An interesting anecdotal note is that Adams, in one of his books,
states that Agfa Brovira #2 is about the same contrast as Kodabromide #3.
He used the "F" (glossy) surfaces but did not ferrotype them. Perhaps this
is after Agfa changed to the ISO system.
CHEERS!
BOB
-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow
Sent: Saturday, July 27, 2013 1:09 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Contrast grades
----- Original Message -----
From: "BOB KISS" <bobkiss@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, July 26, 2013 1:48 PM
Subject: [pure-silver] Re: Contrast grades
> DEAR MARK,
>
> Fasten your seatbelt because, when Richard gets
> home from work,
> he will give you a thorough description of the methods
> used to determine
> paper contrasts for both graded and VC paper.
>
> However, in summary, although there are
> standards of how
> manufacturers are supposed to determine contrast of their
> papers, the
> reality is that, from manufacturer to manufacturer, there
> are significant
> variations of the contrast of both graded paper and VC
> papers for each
> "number" claimed by them.
>
> As long ago as Adam's books, The Print and The Negative,
> he talked about the
> significant variations of contrast of #2 papers from
> manufacturer to
> manufacturer. Recall that his zone system was based on
> trying to produce a
> neg that print nearly perfectly on a "middle" contrast
> paper and he aimed
> his process at #2 contrast graded paper.
>
> I pass the scepter to Richard.
>
> CHEERS!
>
> BOB
Well, I thank you for the compliment but I can't add
much. Both speed and contrast are covered by ISO standards.
Kodak used to explain this in their printing handbook and
paper catalogue. If you can find one used it will give you
details. At one time AGFA used a different system for
indicating contrast. AGFA papers were about one step higher
in number than Kodak for the same contrast, that is, AGFA
No.3 was the same as Kodak No.2. However AGFA went to the
ISO system perhaps thirty years ago. The existence of some
AGFA papers with No.6 contrast grade lead some people to
think they were extra-high contrast when they were the same
as Kodak No.5.
The visual contrast of a paper is strongly affected by
its surface. Only glossy surface can produce the highest
contrast grades. The scattering of light from matte
surfaces reduces both the effective maximum density and the
brightest highlights. Kodak discusses this in their
handbook.
Note also that different types of light sources have a
significant effect on effective contrast. The difference
between a diffusion source and the common semi-diffusing
condenser source (large, diffuse lamp and condenser) is
about one paper grade and the difference can generally be
exactly compensated by changing either paper grade or
negative contrast. True point source lamps have much higher
contrast and often can not be exactly compensated. However,
they are rare.
Another factor in visual contrast is the paper surface.
Again Kodak discusses this in their paper handbooks. Maximum
density range and hence maximum contrast can be obtained
only with a glossy surface paper. The scattering from matte
surfaces reduces both visual density and visual brightness.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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