The Able Tasman National Park is just a short drive from Nelson. You could spend your entire trip photographing in the park. Take a water tight pack, as much of the park is best accessed by boat or kayak--or long hikes. Just google Able Tasman for guides to the park. Also, the valley along highway 6 to the north east of Nelson is quite beautiful. I was in NZ two years ago and had a great time. If you can, try to see as much of the south island as possible. The glaciers and sounds are incredible.