The Agony of HD

HD used to mean something different to photographers. Maybe you just have to be of a certain age to remember when H-D brought to mind Hurter and Driffield. Ferdinand Hurter and Vero Charles Driffield were two Brits who in the late nineteenth century did the pioneering work on sensitometry and densitometry. The logarithmic chart of opacity over exposure is most commonly called the H-D chart with deference to those who did the exploratory work.

Forever after H-D it was possible to make educated attempts at controlling exposure so as to obtain the desired result in the photograph. Tweaks of development and exposure could be used to reshape the toe or shoulder of the curve or change the gamma (slope.) The ultimate practical use of the science of sensitometry these two founded was expressed in the Zone System as developed by Ansel Adams. The Zone System allowed a shorthand technique for photographers in the field to make the best possible use of the dynamic range available in the materials they were using. Similarly, the Zone System provided the technique for translating the dynamic range of the negative into a print which could encompass only about 7 stops of dynamic range.

All that has changed now, possibly for the better, with the current digital techniques. Current sensors allow for resolution sufficient for projecting images on auditorium sized screens. Current sensors provide dynamic range in excess of what can be had with most emulsions. Post-processing techniques allow for subtle corrections to the H-D curve at any point, allowing creative control not possible when working with film. The new techniques may not have sped the process of photography for art. Just as much time is now spent in post-processing with software as was spent in the darkroom, sometimes more. The options in creative control have been expanded considerably. And the smell of photo-chemicals is now largely a thing of the past.

Has the new technology resulted in better photographs, allowed artist’s visions to be realized in a way that was previously impossible? That would be a difficult point to argue. Whatever has been gained and whatever creative controls have been possible in photography with film or digital methods owes a large debt to Hurter and Driffield. Say thanks the next time you see the initials H-D.


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