National Geographic photographer Martin Edström brings you behind the scenes of his expedition to the world’s largest cave, Son Doong in Vietnam, where he and his large team captured the cave in a new and interactive format.
Suddenly, I’m standing knee-deep in a strong river current with jungle all around me. The noise from the water is heavy, it’s strength pulling at my feet. My team members are spread out in front of and behind me, communicating over walkie talkies as we’re hastily moving through the thick Vietnamese jungle in Phong Nha Ke Bang National Park. A team of 40 porters and guides are helping us, speeding towards our destination.
I can’t believe we’re already here, on our way to the world’s largest cave. But let’s back up a bit.
Hang Son Doong in Vietnam is currently the world’s largest known cave. Its entrance was discovered in the early 1990s, but the cave wasn’t properly explored until 2009. Scientists have just begun to unravel its many unique features and describe its specific ecology. The biggest chamber is more than 5km long, 200m high and 150m wide. The cave has two collapsed dolines, or sinkholes, that let daylight in. This has given life to the cave, making it possible for two separate forests to grow within the cave.
Mounting an expedition for photography in the remote wilderness of Vietnam, descending into the depths of the world’s largest cave, is a complicated thing.
Doing this while also attempting to capture the cave in a new and very technically complicated format, is even harder. Now knowing that the expedition turned out a great success, it’s easy to just talk about the final product. But I want to give you some insight into the very complicated process of getting to that point.
I first heard about the cave sometime in 2014, and realized it would be a fantastic location to create an interactive experience, letting people explore it for themselves online. It’s just such an amazing location in itself, something anyone would want to explore.
About the same time, news broke that a Vietnamese tourism company wanted to build a quite intrusive cable car system through the cave, opening it up for a more massive flow of tourism. This was met by outrage from both Vietnam and the world. Suddenly the conservation of Son Doong became an issue, and I knew that if I was ever to do this interactive experience, I had to do it now.
So, after quickly getting help from National Geographic to fund an expedition for me to make this happen, I reached out to a lot of equipment sponsors to help me make this possible. We were going to need a lot. And suddenly, in November last year, we had a pending expedition that had to happen in January, leaving just about two-three months to plan it all.
Now the expedition can be declared a success but there was a time when success seemed doubtful, at best. This was the hardest project I’ve ever planned for, both creatively and logistically. There were a lot of x-factors, mostly due to the fact that capturing images in 360 degrees is such a messy workflow compared to normal stills and video. Here I tell the story of the expedition, concentrating specifically on the technology that made it all possible.
Lighting was the largest challenge because we not only needed to light the cave in one direction, like for still photos and video, but in all directions to capture a 360 degree panoramic image.
We used the fantastic MKR30 lights from X-LED Technology in the Netherlands. These extremely strong yet portable lights provide 44,000 lumens at 300W from 30 separate LEDs and are continuously dimmable. When I first tried them out indoors, the video clip I made shows the daylight outside the windows turning black as the lamps were turned on. They have a colour temperature of 6200K and a CRI of 65. I used two of them with a flood light beam of 90 degree soft spread, and one light with a more focused beam to be able to highlight some features inside the cave with more focused spotlight.
Running on standard Ryobi 18V batteries, these lights were perfect in terms of portability: we could just buy enough Ryobi batteries to get us through the shots in the cave. With a single battery lasting just 20 minutes at full brightness, though, we ended up carrying over 16Kg of batteries just for these lights.
To be able to place the X-LED lights in the tough terrain of the cave, we used the really small and extremely versatile Manfrotto Befree tripods. They are like the acrobats of the Manfrotto family – extremely small and flexible. The perfect tripod to squeeze onto small stalagmites inside the cave, or inside narrow passages where other tripods wouldn’t fit.
Three of my team members were simply running around with these lights at all times, placing them on tripods to light the caverns from atop boulders and stalagmites as I was directing from behind the camera over the radio. We were sometimes spread out as far as a kilometer apart – them sitting somewhere in the dark – ready to flip the light switch on my command. Our radios were absolutely essential to keep this workflow going.
Fortunately, these three lights turned out to be enough to light the caverns. However, they’ve have now been superseded by the even more powerful XHP lights which boasts 50,000 lumens at 320W, 5700K colour temperature and a CRI of 80. I currently have an order set with X-LED to replace my lights with these new ones. I can recommend them for basically all lighting challenges where you need maximum output from the smallest and most portable source.
We had a massive camera setup. I think we brought 25 cameras of different kinds. They ranged from a small, quick-and-dirty solutions – like dropping a camera on a tripod – to bigger cameras with better lenses to cover some shots in higher resolution.
In many locations inside the cave, we photographed 360 degree panoramic images at over 1 or 2 gigapixels, making sure we captured a lot of detail that can later be zoomed into by the reader/viewer. This creates a fantastic layer of interactivity, making it possible, not only for people to walk through the cave at their own pace, but also to look in greater detail at whatever features they are interested in. For these main gigapixel images that make up the largest amount of the 360 images from the interactive story, we used a Nikon D810 with 24mm, 35mm and 50mm lenses. We chose the Nikon D810 as the main camera because of its high resolution for a DSLR – 38 megapixels and a full frame CCD.
Exactly how many exposures are need for a single 360 degree image depends on many factors, mostly of how high a resolution we wanted to create. For the Son Doong interactive story, we often took 200 to 500 source images to create a single 360 panorama. However, that was also because we used bracketed exposures to balance the lighting with something called Exposure Fusion, which is rather like HDR (High Dynamic Range photography).
To capture all these images we used a device called a Gigapan robotic head that we mounted on our sturdy Manfrotto and Gitzo tripods and which moves and controls the camera. It’s simple really: a robot that shoots on my command!
Supporting all of our camera rigs and the X-led lights, we brought almost 10 different tripods for the expedition. The main workhorse were the 2 Manfrotto 190 carbon fibre 4-section tripods that were always supporting our robotic Gigapan heads.
For the lights and other accessories, we used several Manfrott Befree tripods. A veritable swiss-army knife of the Manfrotto family, there’s basically no situation or tricky placement that the Befree’s can’t manage. Very handy, small-sized tripods.
However, my personal favourite – the one always on my backpack in the cave (and in most of my assignments since) is the Gitzo Mountaineer Tripod Series 3 Carbon. It has this minimalistic and extremely rugged aura about it – and is sturdier than any tripod I’ve ever used. So that quickly became the number one tripod for shooting the most important 360 images while in Son Doong.
Shooting in 360 degrees is very different from shooting stills or video since the images don’t come together until stitched in a computer. This means we can’t preview it while shooting. So after spending each full day inside Son Doong, getting multiple locations covered in hundreds of gigabytes of source images, we really didn’t know if the images really turned out well.
It all came down to gut feeling, trusting our camera settings and our view of the lighting of the cave – trusting that it all would come together well once in post-production. So every night in camp (we camped inside the cave for several days) we sat down by our laptops to test-render most of the images. It wasn’t until this point we actually knew if the images had turned out well and could see how it would all come together.
I remember the first time we did this, after the first day of shooting inside the section near the Hand of Dog formation. This was the hardest place to shoot: a massive cavern that can easily fit a Boeing 747 flying through. We did get a lot of light from the X-LED lights, but you never really know how it will turn out once stitched into a final image.
Having used the 38 megapixel Nikon D800 and D810 cameras, we had RAW images of about 45 megabytes that were first converted into 16-bit TIFF format, resulting in source image files of about 200 megabytes. This means that during the stitching of each and every one of these 360 images, about 60-90 gigabytes of data had to be processed by the computer at the same time. This required a serious amount of computing power.
Rendering a 360-picture used to take up to eight hours and we couldn’t afford this amount of time in the cave. But thankfully, due to some incredibly powerful laptops that Dell sent with us, we could test stitch most of these images while inside the cave.
When creating a virtual reality story such as this one, sound is as important as the images. Sound has the power to literally transport you to the place. Listening to the sound gives the website visitors exactly the same feeling as we had in the cave. 360° panoramic views combined with the fantastic soundscape recreate the atmosphere that we experienced in Son Doong. Sound-wise, there was always something to be heard: wind, water dripping, a river running, distant birds. Sometimes also the thundering silence.
The microphones we brought were a Sennheiser SPM 8000 stereo microphone, an MKH 8060 short gun microphone and an MKH 8070 long gun microphone. All three of them are based on Sennheiser’s MKH 8000 series radio frequency condenser microphones, which feature a very natural sound with extremely low inherent self-noise and high resistance to unfavourable climatic conditions, such as moisture, dampness, cold and heat. Basically dungeon-crawler microphones, all of them.
The SPM 8000 stereo microphone was always on recording duty, it was great for capturing the atmospheric audio. We used the MKH 8060 short shotgun microphone about 50% of the time, when we wanted to highlight a sound, for example the singing of birds, or some sounds of the river that flows through Son Doong.
The MKH 8060 was also the microphone of choice for recording the Vietnamese song that can be heard when the virtual expedition reaches the second doline. The short gun microphone is equally well suited to music recordings as it doesn’t suffer from the colourations that can occur with other shotgun microphones. The song is actually sung by one of the guides – he has such a great singing voice. The song was written by a famous Vietnamese composer and is about unity in Vietnam. We thought this would make a great addition to the material. You can hear the song from afar when you get to the second sinkhole; it becomes louder when you continue through the jungle, and fades away when you enter the cave again.
The MKH 8070 was used for about 25% of the recordings to capture far-away sounds – which happened quite a few times in this gigantic cave. It was used to record water dripping, far-away birds, and also to raise some of these sounds above the rushing river.
The Interactive Experience
Coming back from the cave to Sweden we had over 700MB of data – images, video and audio – that we now had to put together to interactive story about Son Doong. Just a few years ago, this would have been impossible. The rendering times to put together these high resolution 360 degree images would have taken forever. But now, thanks to all the new technology, we were able to do the project, on this scale, and bring a fantastic interactive reportage about the cave, for people to explore for themselves.
My goal with this project, and this expedition, was to engage people with the cave and its problematic future. I hope that now the story will not only serve to help people care about Son Doong’s future, but also preserve a copy of it. A digital imprint that you can explore yourself, as if you were there.
You’ll find here the end result: www.nationalgeographic.com/news-features/son-doong-cave/2/
Photography: Mats Kahlström, Sebastian Zethraeus, Fredrik Edström and Martin Edström