Long exposure in the Shaft

About the site

The Shaft is a massive sinkhole in the Mt Gambier region, and the deepest cave in Australia. It’s noted in the history books for the four divers that died there in 1973, an event which contributed to the decision to form the Cave Diver’s Associate of Australia and allow Australian cave divers to self-regulate to prevent further deaths.

From a manhole sized hole in a sheep paddock, there’s an 8m freehanging drop to the water’s surface. The cave is about 20m in diameter at this point, and the walls continue to widen out as you drop into the depths. Directly below the entrance hole is a feature known as the Rockpile. While this would originally have been a high point of the bottom in the natural formation of the sinkhole, the property owners later dropped a considerable amount of rocky substrate down entrance.

At the top of the Rockpile in about 35m of water, the cave is roughly oval shaped. At the two opposite ends, tunnels taper down into the depths. Diving on air is restricted to 40m depth, with occasional trimix dives being run to 60m depth. Your first dive in the Shaft is guided, with a swim out from the Rockpile to Sawtooth Rock, a natural feature sticking up to 35m. From Sawtooth Rock you can look back towards the Rockpile and hopefully appreciate the shaft of light that gives this site its name.

Achieving the spectacular sunlight shaft down through the water to the rockpile takes both luck and good judgement. As well as prayers to the weather gods for clear skies, over winter the angle of the sun means direct sunlight does not penetrate the cave. By mid summer the sun is more directly overhead, and the middle of the day is the prime time.

The Shaft was used for the location filming of the movie Sanctum, and the underwater movie lights used on that occasion were run from a three phase diesel generator up top. Even with that amount of power, we struggled to see very far into the depths. While diver bubbles have removed the dark coating from the walls in the shallows, the deeper walls are pitch black. The sheer size of the hole and the dark walls absorb any torch or strobe light – a distinct issue for photography.

About the dive

My intention for this dive was solely photographic. Given it was the middle of winter, I knew the shaft of light was unlikely. However, I was hoping that by taking a tripod down to Sawtooth Rock, I’d be able to do a long enough exposure to capture what ambient light there was. Swimming around with a weighted tripod makes other photography more difficult, so my focus was clear.

About the shot

On the first dive of the morning I’d set the camera focus manually. Reviewing my shots, I’d discovered there was almost no ambient light, and what could be seen was out of focus. A quick surface interval let me up the ISO, move to automatic focus, and increase the exposure time to 30 seconds. A 10 second delay on the camera allowed me to swim out in front of the tripod, lighting the nearby scenery with my primary torch, and this shot is the best of the bunch.

For those divers who’ve been there, this is a great shot. For the vast majority of the world who haven’t, it looks like a pile of pebbles in the dark. For scale, the Rockpile is over 10m high before the natural rock starts, and the black walls are at least 30m away on the closer sides. I’m keen to return to the Shaft in mid-summer and have another go with this setup, hoping to get some definition of the cave walls.