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What is the difference between 100 ISO film and 400 ISO film?
Yah, I know, 2 stops.  What I mean is, what difference is there in the production of the emulsion between the two. For example, to keep it simple, between TMax 100 and TMax 400?
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Fundamentally, grain size and Iodide level.
PE
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 Originally Posted by Photo Engineer
Fundamentally, grain size and Iodide level.
PE
And two stops.
Rick A
Argentum aevum
BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"
"Political correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."
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A little off topic here, but why is there no 800 speed B&W film? I've always been curious about that.
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Probably because shooting ISO 400 @ EI 800 requires only a one-stop push?
website | Flickr"Embrace the negative with absolution, your final positive reward." --IQ, "The Province," Frequency
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Originally Posted by Photo Engineer
Fundamentally, grain size and Iodide level.
PE
Thanks. Is it both these, or primarily one of them that requires the longer time in developer?
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Originally Posted by Photo Engineer
Fundamentally, grain size and Iodide level.
PE
Thanks, I suspected but was never sure.
Steve
Warning!! Handling a Hasselblad can be harmful to your financial well being!
Nothing beats a great piece of glass!
I leave the digital work for the urologists and proctologists.
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How is grain size controlled in manufacture?
If larger grain size causes faster film, I assume that means it's harder to make grainy film than fine grained film. That doesn't seem quite right.
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I believe the emulsion pre coating solution is started by bring the pot to a saturated level at some critical temperature, and then 'ripening' i.e. holding it a some stable temperature to aloow the crystal sizes to grow.
This is gross simplification, but rather a way to understand how differnet sized grains could be formed.
I believe the challenge is to make it not self fogging, stable, and sensitize it at all colours, and still compatible in performance lot to lot.
There is a lot of inter vat blending of fast and slow in most emulsions, I think, and it is the ratio that determines the effective speed.
A purchase and read of the advertised 'Making Kodak Film' is a good start to understanding the complexity of this product that we accept as a given manufactured good.
my real name, imagine that.
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All of this has been described in detail in the Emulsion Making and Coating forum here on APUG. Basically, grain size is a function of addition time, holding time, reactant concentration, ingredients, and addenda among a few of the variables. Others are gelatin concentration and type, and the phase of the moon! 
My book will give more detail on this than in the Forum here and in Bob's book. And yes, I am working on it. It is here in Word, on my screen behind my browser! I am editing page 124 right now.
PE
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