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High Dynamic Range (HDR) imaging tends to get a bad name for itself in the field of landscape photography. Certainly, when misused, it can lead to flat or surreal looking images. I'm not normally a fan of HDR, but this sort of sea cave photography is an ideal application for the technique. Indeed, many of my cave images could not have been created without it.
Aside from the hazards associated with getting to the locations, the big technical challenge with this type of underground work is the extreme contrast. The cave mouths are very bright whereas the interiors are very dark indeed. Some of these caves in County Antrim are so deep and dark that I needed a head-torch to work my camera controls (and to watch out for any ghosts).
The HDR process involves taking a number of differently exposed frames and combining them in Photomatix or similar HDR software. For the deepest of my cave photographs I had to merge 7 photographs spanning exposures of 30 seconds up to 1/30th of a second (a whopping 10 stops !!). Even with a 30 second exposure, the deepest cave shadows were often pitch black. The exposures were frequently made even more difficult by the blooming of the sea haze in the cave mouths.
At home, I used the Photomatix software to merge my range of exposures into single HDR tonemapped image. It was then a matter of adjusting the black and white points as well as manipulation of the tone curve to boost contrast in the dark areas. Some final localised dodging and burning were used to bring out the key parts of the image and also to suppress the sea haze in the cave mouth. My aim was to create a set of photographs that held a similar mood and feel to the old Victorian artwork while also using the more modern digital techniques to bring these views into the 21st century.
by Andy McInroy
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