Subject: A light-coloured Coral Grouper (Cephalopholis miniata) dashes into a shoal of Goldbelly Cardinalfish (Apogon apogonides). Groupers are piscivores and will venture around coral heads and bommies where food is abundant and the pickings are easy. The Cardinalfish in their turn apply the principle of safety in numbers.
Technique: When filming scenery where the subjects are at different distances from your camera’s lens you will have to increase your depth of field. This is achieved by increasing your f-stop (= reducing your aperture). A side effect of a larger f-stop/small aperture (smaller opening on your camera’s diaphragm) is that less light is entering your camera and therefor you will have to increase the intensity of your lights or increase your ISO.