Vietnam’s Sơn Đoòng Cave is the world’s largest at over 5km long, 150m wide and, at its tallest, over 200m high – able to accommodate the Statue of Liberty twice over. Estimated to be 2-5 million years old with a fast flowing subterranean river, it only became internationally known in 2009. It’s the perfect subject for WOWOW Inc’s 4K documentary series with an experimental 8K broadcast. For the documentary, Sony’s FS7 II Super 35 camcorder was the production’s first choice. Able to shoot high quality 4K at a cinematic 23.98P, the FS7 II is also robust enough to withstand the harshest conditions and has an ergonomic design ideal for shooting on uneven terrain. Alongside the FS7 II, an α7S II was used for shooting in ultra-low light conditions. We talked to production director Sota Koshino and camera operator Masahiro Hariu about their impressions of the FS7 II.