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What is the relationship between film speed VS contrast?


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#1 Michael Boe

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Posted 30 January 2010 - 12:27 PM

Hi,

I'm currently studying cinematography at film school, and for a short horror film I'm working on I'd like a more contrasty stock. Am I correct in thinking that slower speed stocks are generally more contrasty than higher speed stocks? I know that higher speed stocks are more grainy. Thanks in advance.
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#2 John King

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Posted 31 January 2010 - 01:06 AM

Hi,

I'm currently studying cinematography at film school, and for a short horror film I'm working on I'd like a more contrasty stock. Am I correct in thinking that slower speed stocks are generally more contrasty than higher speed stocks? I know that higher speed stocks are more grainy. Thanks in advance.



Hello,

Yes, the slower the film speed, the sharper the contrast (an better transfer results in electronic formats) higher film speeds are generally more grainy. Best results are to shoot slightly over-exposure (with colour stock) to get a denser negative so that blacks do not look muddy in shadowy areas. Hope this helps!

God Bless!

J.M. King
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#3 Dirk DeJonghe

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Posted 31 January 2010 - 01:17 AM

Generally speaking, manufacturers try to match the contrast of different speed stocks in the same film family. For example you can intercut Vision 3 7219 and Vision 2 7201 easily. On the other hand both Kodak and Fuji have 'outsider stocks for special tastes' like the Fuji Vivid family with extra contrast and saturation and the Kodak Vision Expression with intentionally lower contrast and saturation.

Kodak has currently three different 500 speed stocks: the 'normal' 5219, the 'lower contrast and desaturated' 5229 and the 'snappier' 5260.

So the conclusion is that variations in contrast are due to market demand and perceived taste of the times rather than film speed.
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#4 Satsuki Murashige

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Posted 31 January 2010 - 04:05 AM

Am I correct in thinking that slower speed stocks are generally more contrasty than higher speed stocks?

This is partly a perceptual thing- when you shoot high speed stocks, you're typically working at lower light levels, where the ambient light that is always bouncing around becomes proportionally stronger and acts as fill light. So that can give high speed stocks the impression of being lower contrast than slow stocks of the same series.
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#5 Paul Bruening

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Posted 31 January 2010 - 03:12 PM

"What is the relationship between..."



The worm is the spice. The spice is the worm.
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#6 John Sprung

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Posted 01 February 2010 - 03:16 AM

Dirk has it right. Contrast and speed can be varied independently in the design of emulsions. High contrast requires a very small range of grain sizes. For low contrast, you want a wide range of grain sizes. Slow film requires small grain, fast film requires large grain.

The reason for all this is that the number of photons required to expose a grain is the same, no matter how large or small the grain is (IIRC, its something like six photons). The bigger the grain, the more likely it is to get hit enough times. From that, you can figure out all of the above.




-- J.S.
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