In November 2016 I was commissioned to go to New Zealand to capture the famous underground Glow Worms, on camera. This was by far the most challenging and adventurous shoot I had the fortune of being faced with.
Having never heard of these glow worms, the company who commissioned me, sent me over a couple links to videos that had been taken of the glow worms, which I was excited to see. However right when I opened the links I immediately knew there was an issue- These videos were not recorded video clips taken and edited, these were time-lapse photography sequences that were edited together to look like continuous video. I reached back out to the company to make sure they knew how these images were taken, and they let me know they do not want time-lapse photography, but want video to match a similar style that they usually go for.
Light-the first Challenge
The first and most obvious challenge to me was that these tiny bioluminescent worms live in complete darkness and only let off a very minimal amount of light. And since I don't live in NZ, and can't get a reading of their light levels or perform camera tests, I needed to figure out how much light these worms truly put off. First thing I did was search to see if any other filmmakers had captured these worms on camera in a cinematic way before. The first video that popped up was an amazing motion time-lapse photography video and luckily the photographer put up the exposure information. He was doing a minimum of 30-second exposures and best case scenario using a very fast f/1.2 lens at an ISO of 1600. So I immediately crunched the math to equate that 30-second exposure to a 1/48 of a second exposure that a video camera would take. Essentially to get a similar exposure I would need another 10 stops of light in order to match his exposure, and since I have to keep my shutter speed at 1/48th, my only choice is to crank my ISO up to 1,600,000- which was out of the question. So I did what I could and got the best high resolution low light camera on the market- the Sony A7SII. You can comfortably shoot with this camera at a whooping 40,000 ISO, which is fantastic, but still only gets me 5 stops more of exposure to the 10 that I would need.
Ratios, Ratios, Ratios - mirroring our eyes
Video Camera sensors are getting more and more sensitive to light, which is incredible, however, it's going to still be a little while before a video camera can capture the same amount of light as a long exposure photograph. The beauty of long exposure photography is that it keeps the same ratio of light in your scene as you would have naturally. For instance, the light the glow worm is emitting in relation to the ambient light in the cave- When you look at the worms with your eyes, the brightest thing in the cave is the glow of the worms, so when you go to capture it on camera you would want to mimic how it looks to our eyes. So if it's too dark for your camera to capture, and you take a long exposure for lets say 30 seconds, then for 30 seconds the camera is taking in all the light it can that is already present (glow worm light and ambient cave light). However if you were to add an artifical light to the scene, all you can do is brighten the background, you cannot control the brightness of the glow worms light and in order for it to look natural, as we see with our eyes, you would want the brightest thing in the scene to be the glow worms light- so how do you film the glow worms to mimic how we see them in real life if your camera is not sensative enough to capture the light emitted? Well that's when creatively you have to make a choice and when you add a light you end up throwing off the natural ratio of light causing it to not look natural. And since you're doing video and you cannot adjust your shutter speed to do long exposures, then you would need and you try adding a light, it will over power the
They were spectacular, but the beauty of time-lapses photography is that you can adjust the shutter speed of the camera, enabling long exposure photographs. This technique is how the milky way is filmed in most videos- it's actually a series of photographs (24 per second) to be exact. of The only video that came up was from the BBC that was filmed in 2006, and it was obvious they just used artificial lighting on the worms to film them, which is unfortunate because the beauty and draw of them is how much they pop/glow in the darkness.