There are a lot of caves on this island. Much of the island of Hawaiʻi is riddled with lava tubes. Hiking or riding the trails or back roads of the island often offers a mysterious opening into darkness. Not that I explore too far, I am not a hard core spelunker. But I do often poke my head in to see what the cave has to offer.
Often when I reach a cave I am not carrying the necessary equipment to explore or photograph the cave. There are a few things I always have with me… A camera of course, I am rarely found without one. There is always a good flashlight in my pocket, a bright little LED light with a lithium battery. These two things are all one needs to get a photo of a cave.
Unless the cave is quite small the camera flash will provide unsatisfactory lighting of the cave. The flash will also tend to light up nearby parts of the cave and leave anything at any distance poorly lit. I generally do not use a flash in a cave unless I am photographing small features close at hand.
The technique is simple… Set the camera on a tripod, or a rock, and open the shutter for as long as the timer will allow, usually 15 or 30 seconds. During the exposure you paint the cave with light. Simply wave the light around in a random pattern, never letting the beam rest too long in a single place to evenly distribute the light. This simple method will allow even a large cave to be illuminated with a relatively modest light.
You will need to do this a few times and adjust your process to suit the situation. You can adjust the camera shutter timer or gain (ISO) to adjust the exposure. You can decide where to spend more or less time with the light if there are dark areas or hotspots in the image.
There are a couple tricks… The further away sections of the scene will require more light, spend more time illuminating the furthest sections of the scene. If the light is located too close to the camera there will be few shadows to provide depth and texture to the scene. during the exposure step to the side a little or keep the light close to the cave floor so the low rocks cast shadows.
Focus can be difficult. Set the camera for a smaller focal ratio, perhaps f/5.6 or f/8 to keep a good depth of field. Hold the flashlight on a feature well into the scene and focus on that. Some trial and error may be needed to get a good focus.
It can be fun too! When exploring the lower end of Thurston Lava Tube I was all set up with the camera and tripod when a group of kids arrived. Curious as to what I was doing I showed them. During the exposure I had the whole group wave their lights around as we all stood behind the camera. The kids were amazed when the photo appeared on the LCD display, they had no idea you could light up a cave and take a photo with a bunch of little flashlights.