Cave photography and lighting pools of water.
I'm about to go caving for a week and among other things there will be some areas I'd like to photograph that have pools of water of varying sizes on the cave floor. I'd like to try photographing these areas by placing a flash unit (or a light) under the water, such that it lights up some of the pool from below. The thing is, I've never attempted something like this before and I can't find much information on how best to go about it.
Here's what I'll have available for camera and flashes:
- 1 x Canon 5D Mark III
- 1 x 550EX Flash. GN58 (~5600K)
- 2 x Yongnuo YN-500EX Flashes. GN53 (~5600K)
- 4 x YN622C radio triggers
I also have the following handheld flashlights:
- 2 x ZebraLight flashlights. Neutral white LED, 1000 lumens each (~4400K)
- 1 x Nitecore EA2 flashlight. 280 lumen (~6500K)
- 1 x L3 Illumination L10 flashlight. 120 lumen (~4500K, high CRI)
- 2 x TrustFire X6 SST-90 2300 lumen flashlights (~6200K, probably only really ~1000 lumens each)
I have CTO 1/8 and CTB 1/4 gel sheets so I can get most of the light sources to roughly the same colour temperature if required. It probably won't matter for the underwater lighting since the water is apparently a greenish tinge anyway. I'd like the green to show in the photo but accuracy of the green doesn't really matter.
The ZebraLights, Nitecore and L3 flashlights are all waterproof enough that I can submerge them for 30 mins or so without issue. I also have one waterproof bag I can fit a flash unit in for use underwater.
The cave is huge (HUGE!) and I'll be trying to use people for scale as much as possible (they'll have their own headlamps and flashlights). This may limit my shutterspeeds somewhat since people will need to stay still for any long exposures. I'll struggle to light much of the cave with the flashes since the cave is so big (up to 200m wide and high in places, but there are also areas where the cave roof has collapsed letting in natural light from above).
Given all that, I clearly have a lot to think about. Here are some examples of the questions I have:
- Would it be better to put a flash in the pool or a flashlight? I like the idea of a flash because I could selectively disable it to also try shots without the pool being lit, plus I wouldn't be wasting precious flashlight battery the whole time I was getting set up. But will the radio trigger work underwater, would I be better off using the flash to light the cave instead, etc.
- I assume I'll be best with the flashes always in manual at full power rather than E-TTL?
- What sort of exposure would I need for a 1000 lumen flashlight to equal the light given off by a flash at full power?
I realise a lot depends on the exact environment and the types of shots I'll be taking, but any general advice, suggestions and tips that might help for this scenario (and cave photography in general) would be much appreciated.