Jan 232012

Beams of light in the Shaft

About the site

The Shaft is a site that I’ve talked about twice before. From a manhole-sized hole in the middle of a paddock divers are lowered to the water’s surface 8m below. After gearing up in the water you drop into the depths below – the central rockpile and debris cone starts at 35m, and the cave gets down to over 100m on one side.

The walls are predominantly black and the small entrance means there’s very little natural light in the cave. Dive lights struggle across the huge distances. In summer the angle of the sun allows rays of sunlight to pierce the darkness. The ambient light coming straight down the hole is enough for the human eye to take in the whole scene. Cameras are a little more demanding, and I’d struggled on two previous occasions to capture what I could see.

About the dive

The previous dives here with the camera had been in winter with a very low sun angle, and in summer on an overcast day. In both cases I’d managed to illuminate the central rockpile, and the second time a long exposure and repeated strobes by a diver had revealed some of the details of the walls on each side. The most spectacular aspect of this site is the shaft of sunlight that it’s named after, and I was keen to capture both the beam and enough of the surroundings to explain the distances involved. The morning again dawned dim and cloudy, but some anti-rain dances produced blue skies by 11am. Calculating for daylight savings time we were in the water just after midday. I descended to Sawtooth Rock and set up my weighted tripod, while my two buddies hung about in the shallows of the sunbeam.

Hanging in the shaft of light

This shot required a tripod for a longer-than-handheld exposure, and I found the right angle and pointed the camera up at the beams from 38 metres down. To help with the mission I was using light trimix mix to reduce the effects on nitrogen narcosis on my exposure calculations. I tried two different spots for the tripod before moving back to the one I had used for the last shoot and signalling to my buddies to descend down the light beam.

About the photo

My major investment for this dive was three bathroom mirrors from the cave diving aisle of Bunnings hardware store. Careful arrangement with duct tape and bits of string in the paddock above angled the extra beams down into the cave. The beam on the right is the original, and the three smaller beams on the left are reflected sunlight. I also changed the focus settings on the camera so that auto-focus was linked to the AF-on button and not the shutter button. This meant I focused the camera on the rockpile before putting the tripod down and then didn’t have to worry about locking the focus for each shot. From here (with the help of the trimix) I was free to concentrate on shutter speeds and apertures.

This shot was taken over 3.2 seconds, at f8 to avoid soft corners with my rectilinear wide angle lens. This has given me enough ambient light to outline the distant central rockpile without overexposing the sunbeams against the dark walls. I was hoping for a recognisable diver silhouette in the light, but 3 seconds is a long time to hover without moving or breathing – especially when the model can’t tell when the picture is being taken! If you look closely, the two divers do provide a sense of scale in this massive space. My next thought is to use a strobe to outline a diver in the dark for an instant, eliminating the problem of diver movement. Combining this with the beams and a little more light on the rockpile would be perfect…something to try next summer solstice.

  2 Responses to “Long exposure in the Shaft III”

 Leave a Reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>


(required, will not be displayed)