Colour Underwater

The physics and theory behind underwater photography is quite interesting. What you don't really appreciate until you see if for yourself is the fact that the behaviour of light underwater means that colours get "lost" from the light spectrum the deeper you go, with reds the first casualties. What this means is that unless you use artificial light (ie strobe/flash) to put back the natural colours, your shots will have a green or blue cast, depending on the kind of water you are diving in. This is well illustrated by these 2 photos from today in Loch Fyne. The top one was taken on automatic (I had left the camera on this setting by mistake after having taken a bit of video) and without using any flash; the one below it is taken on manual settings with full strobe (1/100 at f18 and ISO 160, strobes on TTL). Strangely, the colours I saw were not as green as the top photograph because the brain tends to compensate a bit for the cast; so what I saw was somewhere between the two images. As for the dogfish, he swam away before I could go back to video setting so no footage was got!