F tunnel in Tank Cave

About the dive

Tank Cave is a labyrinthian maze of intersecting passages, located in the Mt Gambier region of South Australia. First dived in the 60s, the challenging narrow and silty entrance meant exploration didn’t truly begin until the 1980s. Today, the cave has approximately 11km of mapped passage. The main tunnels run on an approximate NW-SE trend, and the cave develops a distinct character in the different areas. The tunnels are named by letter and number, and tags are placed in the cave on the permanent lines at key points to aid navigation.

Tank Cave is generally shallow, with most tunnels being between 10m and 20m deep, allowing for long dives. This photo was taken in F tunnel, which is well suited to photography with more space than some of the sidemount only areas of the cave. The spectacular sunken floor also appeals to me – you can see where the cave may have once had tunnels at multiple levels, and the floor has collapsed into this space. In other tunnels in Tank Cave, you can see potential lower passages filled with sediment.

F tunnel is also generally straight, and stays mostly the same size and colour. Changing tunnel size or rock colour is more challenging for photography, given the variations in settings and light required. Larger tunnels and darker walls bounce less light back. Of course, once you’ve upped the strobe power and travelled around one more corner into a smaller area, your next shot ends up blown out.

This dive was a dedicated photography dive, and we also intended to place Ken’s pinger at the end of F tunnel to aid with mapping. The white, circular end of the pinger can been seen positioned between Ken’s tanks for the journey. Both Ken and Ag are wearing their tanks sidemounted (as opposed to on their backs), and there are large areas of the cave that can only be accessed using this configuration. This particular dive was the first of the weekend, and the cave hadn’t been dived the previous two weekends. With the amount of time since divers had been in F tunnel, the water was crystal clear without any milkiness or silt to create backscatter.

About the shot

This shot was taken about halfway down the tunnel, in a series that takes advantage of this stunning cave. I would swim out in front, turn around, and capture a number of pictures as my models swam towards the camera. This was the first time I’d dived with the camera in Tank with Ken and Ag, and the first few times I turned around Ag would stop midwater and pose at a distance instead of swimming. Once we’d sorted that out, I moved onto partly intelligible hand signals to try and get the distances (camera to Ag, camera to Ken, Ag to Ken nose to fins, Ag to Ken sideways) and heights of each of the three of us in the tunnel right.

The key with multiple models in straight tunnels is to achieve both excellent lighting of the back diver from the strobes carried by the front diver, and adequate separation so the viewer can clearly make out two divers instead of one amorphous blob. This is especially challenging with sidemount divers, who don’t have an obvious twin tank setup on their back to draw the eye. Achieving other aims like clear facial expressions and avoiding bright spots from off camera strobes is a bonus!

This shot was really helped by Ag’s previous modelling experience with Wes Skiles, and her impeccable bouyancy and trim. For the record, this was her standard “I’m exploring a cave” expression, generally employed when cameras are around. Ken’s beautifully coloured suit and jacket made a real difference to him showing up in the shot instead of blending into the wall. Ideally, I’d have waited another 2 seconds for him to finish his exhalation in the top photo – the challenge of co-ordinating multiple models and their ongoing need to bubble.