Braided rivers are compelling photographic subjects. New Zealand is one of just a small number of places where extensive braided river systems are found. They are normally associated with wide valleys adjacent to mountain ranges, formed by the constant movement of silt, gravel, and other sediment erosion washed down the mountain slopes.

Photographing from a helicopter with the doors off, as I did here, can be tricky. A biting wind screeching through the cabin renders your fingers numb with cold, and the helicopter's movement and vibration make holding the camera steady and level a real challenge. Without the obstruction of the doors and windows, we can shoot at wide angles and point the camera straight down, but we still have to be careful to keep the rotating blades out of the frame.

The best time to shoot is early in the morning. Here in the Tasman Valley, the optimum time is around 45 minutes after sunrise, by which time the sun has risen sufficiently above the surrounding mountains to light up the valley but is not so high as to create unwanted glare and specular highlights on the water. There is a window of time when the river appears bright blue. Too early, and it appears silvery grey; too late, and the colour contrast between the river and the gravel beds is lost.

The scope for adjusting camera settings whilst in flight is very limited (not least because your fingers are so numb!)., so I always set my camera up to shoot at a wide aperture (depth of field is not an issue), a very fast shutter speed to compensate for the movement of the aircraft, and to control overall exposure in the fast-changing light conditions with ISO set to Auto and autofocus on.

Handy tip: With a mirrorless camera, you can clearly see the blades turning in your viewfinder, whereas, with an optical viewfinder, they are barely discernible, such is the speed of their rotation.