Nov 072011

Kilsby's Sinkhole

About the site

Kilsby’s is a Deep Cavern site in the Mt Gambier region, reaching depths of 60m in the back corners. It’s renowned for the crystal clear water normally only found under a roof, as sunshine in freshwater encourages algal growth. The daylight zone is huge, and you can look across a space the size of a football field and watch divers hanging out on the far side. The centre of the sinkhole comes up to under 20m depth, and as it gets deep on each side you swim under a roof, and can look back from the dark into the daylight.

About the dive

On this particular occasion, KA and I had already done two dives in Piccaninnie Ponds that morning, and we were doing a shallow third dive here to round out the afternoon. It was early spring, and I was surprised to see baby ducklings making peeping noises as they swam around the surface of the sinkhole. Their mother duck had decided this was a safe place for her to nest, but she hadn’t counted on the divers turning up every couple of weekends. I got some interesting shots of the underside of the duck family before surfacing.

We were still closer to the winter solstice than the summer one, and the high sides of the sinkhole meant there wouldn’t be many direct beams of sunlight down through the water. It was a sunny day however, and as we got in I was hoping to get some shots contrasting the dark zone against the background of diffused underwater sunlight.

Ducks in Kilsby's SinkholeAbout the shot

For your average (dark) cave dive, shutter speeds on the camera are not something to worry too much about. Changing the shutter speed impacts on how much of an ambient light source (sunshine, dive lights, etc) is captured in the picture. Light from a strobe is a rapid one time event, and leaving the shutter open longer won’t help you capture more of it. Given this, I normally use a shutter speed of 1/160, and alter my f-stop to achieve the right exposure.

Of course as soon as daylight enters the picture, this all changes. Having adjusted my f-stop appropriately in this picture for the foreground exposure, I discovered that the weak winter sunshine filtered through the fresh water was not doing the job. Slower shutter speeds were called for, yet being this shallow in the cave meant I had no floor to brace against. As you can see in the picture, the other divers swimming through the background have an artistic and dreamy quality, otherwise known as motion blur.

With KA in the foreground almost completely in the dark and only lit by my strobes, her motion was frozen by the flash of light from my strobes. You can also see the slow shutter speed has captured the beam of her torch through the water. While water does stabilise the camera, swimming in midwater doesn’t provide the same stability that standing on solid ground gives. Buoyancy and breathing control aside, there’s only so much that can be achieved!

I had taken a tripod with me on the dive in anticipation, but at 10m depth I was nearly 30m from the bottom in this location…my standard tripod was not going to cut it. This shot was taken at 0.3s handheld, and unfortunately the fuzzy sunlit scene behind only gives an impression of the view I could see with my eyeballs. All of which means that more light is required, and this is another setup to retry over summer (with success in Jan 2011, chronicled here). There’s always more diving to be done.

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