Gamma 1?

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Keith Tapscott.
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Location: Plymouth, England.

Gamma 1?

Postby Keith Tapscott. » Sun May 14, 2006 9:04 am

I have noticed in some of the post by Lowell Huff, that he refers to the Clayton F-60 and F-76 Plus products as "Gamma 1" developers.
What exactly is meant by this description?


Digitaltruth
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Postby Digitaltruth » Tue May 16, 2006 12:32 pm

Hi Keith,

Lowell Huff has provided this information about Gamma 1:

Gamma is physically defined as the measure of the longest straight line
portion of the characteristic curve. Idealized, this is a 45? line that
bisects the quadrant. Unexposed but developed film has a low density known
as film base + fog. The useable area of the curve begins at .01 density
above the density of film base + fog, where the film still has a low
gradient and thus LOW CONTRAST. The shadow area of a subject will record on
this low contrast 'toe" of the curve. The central part of the curve is a
straight line. The longer this line is, the greater amount of information
that will be recorded on the film. Above a certain amount of exposure the
curve begins to level out(shoulder), which is why over exposed negatives
often get low contrast highlights. A gamma 1 developer will provide the most
latitude to the toe and central portion of the curve. Ultimately, Gamma is
another way of describing contrast.
--Jon Mided

Digitaltruth Photo
http://www.digitaltruth.com

Keith Tapscott.
Posts: 506
Joined: Tue Jan 17, 2006 8:58 am
Location: Plymouth, England.

Postby Keith Tapscott. » Wed May 17, 2006 12:32 pm

Thanks for the explanation Jon. I`m familiar with the meaning of Gamma, Contrast Index and G-Bar and fine-grain or acutance developers etc, but not with the term "Gamma-1" type developer.

Kino
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Joined: Thu May 04, 2006 8:27 pm

Postby Kino » Wed May 17, 2006 9:46 pm

Keith Tapscott. wrote:Thanks for the explanation Jon. I`m familiar with the meaning of Gamma, Contrast Index and G-Bar and fine-grain or acutance developers etc, but not with the term "Gamma-1" type developer.
I am only guessing, but he is probably referring to the developer being a "unity gamma" developer; a developer that is formulated to create a near 1 to 1 increase in density when processed at "normal" times.

Typically, you process "normally" a .65 gamma, a one-stop push being a .75, a one stop pull being a .55 gamma. These gammas are, in effect, compressive of the overall scene brightness, but unity gamma does no compression (or expansion for that matter, as in positives made from "normal" negatives in motion picture work; typically a 2.20 gamma or higher).

Unit gamma stocks are typically used in duplication work where the material being copied must rigidly maintain they actual contrast index throughout the copy chain.

It is a poor explanation; sorry.


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