I find I use 18mm-c24mm when taking pictures from the cockpit, I don't think I'd need much wider (10mm is about the shortest focal length you can get) and that usually gets a good landscape shot. The same applies for landscapes from the ground. 200mm would be OK for airshows, perhaps you might want more. I would go for the D40, Nikon make very good cameras and it might just have the edge over the Pentax on picture quality.