Talking of Contrast

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29 May 2004 - 1:02 AM

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tim franklin

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29 May 2004 - 5:05 AM

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In terms of film and paper, contrast is simply the brightness range from shadows to highlights that can be held without blocking up or burning out. Its normally expressed in logarithms, where a ratio of 2:1 is a difference of one stop, 4:1 is two stops, 8:1 is three stops etc.

Research by Kodak claimed to show that the average brightness range is 128:1 or seven stops. It has been pointed out though, that contrast varies according to what latitude on the earth you are at - its much higher in the tropics, and reduces the further north (or south) on goes.

Slide film has a narrower range than negative film, typically around 5 stops, where a neg film might be able to hold 7 or 8 stops. A decent B&W paper can hold around 6 to 7 stops IIRC, but paper can be had in varying degrees of hard (more contrast) or soft (less contrast) to suit the subject. Digital has a visible range similar to slide film, though it is possible to extract great detail from dense shadow areas.

In terms of lenses being described as contrasty, its a matter of edge contrast or acutance. A contrasty lens will render a pair of lines - one black, one white - as just that, whereas a less contrasty lens will render them as shades of grey. Hope this helps.

adammalski

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2 Jun 2004 - 6:44 AM

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Tim

Thanks again for helpful insight. Funnily enough after I posted my question, a New Zealand photographic journal gave me some info,which is inline with your comments, so thank you. I look forward to posting my NZ shots on my return in July.

Adam