I just got finished my octocopter with Arducopter electronics. It is built to carry DSLR and should fly 7-8 minutes with 1000g payload. Copter is actually just a quad which has two ESCs and motors on each end. It proved to be really stable platform on first tests last weekend.
I fly with 5000 mAh 14.8V Lipos and have eight 750kv/100W motors. Still the flight time with such a heavy camera will be short. But actually from previous experience I know 5 minutes is long enough for photographing a target. After that you can land, change battery and make a plan for next 5 minute flight.
Images of my build can be found:
and first flights:
Youtube -video shot from another Oktokopter: