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The lower the iso the higher the contrast
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PostPosted: Sun Sep 25, 2016 5:40 pm    Post subject: The lower the iso the higher the contrast Reply with quote

"Films manufactured with very fine grain will almost invariably have relatively high contrast, high resolution and low speed"
Ansal Adams , p.19 "The negative"

Can someone explain me why is that ? I thought contrast is a characteristic of film and not necessarily linked to the iso.
Alex


PostPosted: Sun Sep 25, 2016 6:36 pm    Post subject: Reply with quote

one more question from the book.
"Why overexposing increases grain?"
I would expect a 10 stops (example value) over exposure to give me just plain white
Alex


PostPosted: Sun Sep 25, 2016 7:43 pm    Post subject: Re: The lower the iso the higher the contrast Reply with quote

alaios wrote:
"Films manufactured with very fine grain will almost invariably have relatively high contrast, high resolution and low speed"
Ansal Adams , p.19 "The negative"

Can someone explain me why is that ? I thought contrast is a characteristic of film and not necessarily linked to the iso.
Alex


ISO is a characteristic of any film emulsion. You'll note in the Ansel Adams quote, he's referring to properties of fine-grained films, one of which is low speed.

It sounds to me as if you're attempting to apply a digital mindset to film and its properties. It doesn't work that way. Film is an organic medium with properties that are intrinsic to its physical make-up. Now, as to why these properties are directly associated with each other, I can't explain that because I'm not a chemist. Perhaps someone here can.


PostPosted: Mon Sep 26, 2016 1:07 am    Post subject: Re: The lower the iso the higher the contrast Reply with quote

alaios wrote:
"Films manufactured with very fine grain will almost invariably have relatively high contrast, high resolution and low speed"
Ansal Adams , p.19 "The negative"

Can someone explain me why is that ? I thought contrast is a characteristic of film and not necessarily linked to the iso.
Alex


In a low ISO film the silver halide grains are small and have more or less uniform size. This means the grains have similar individual sensitivity, which results in high contrast. The silver halide grains of a high ISO film have large dispersion of size distribution, and so large dispersion of sensitivity, which results in lower contrast.


PostPosted: Mon Sep 26, 2016 12:21 pm    Post subject: Reply with quote

(I agree I have a digital mindset that I need to overcome)
So the smaller the silver halide grains that it means that I have faster transitions between light and dark areas (so you have higher perceived contrast) while in slow iso the halide grains are larger that smoothes out transitions.
Would I perceive that right?
Alex