by Andy McInroy

Great Sea Caves of Antrim
Appendix 2
Sea Cave Photography using HDR Techniques

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 can be as bright as a summers day whereas the interiors can be 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).

High Dynamic Range (HDR) landscape photography often gets a bad name for itself. When misused, it can lead to flat or surreal looking images that are far removed from reality. I'm not a regular user 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.

The HDR process involves taking a number of differently exposed frames and digitally merging them in computer 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 of exposure spanning 18 stops of dynamic range!!). 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 light in the sea haze at the cave mouths.

At home, I used a piece of software called Photomatix 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 structural parts of the image and also to suppress the sea haze in the cave mouth.

The High Dynamic Range (HDR) Process
© Andy McInroy

My aim with this project was to create a new 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. The project is therefore mainly based on a monochrome approach. However, you will also see some colour versions which hopefully will give you some idea of the huge variety of tones that exists in these caverns.

Portcoon cave film
Film and screenshot © Des Henderson

Des Henderson, a Northern Ireland based film-maker, has created this short documentary film on my Antrim Cave photography. It gives a superb insight into these hidden places and the difficulties involved in photographing them. It also demonstrates how the HDR exposures are made in the field.

To view the film, follow the link below.

Portcoon Cave film
by Des Henderson

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