I took a sunset cruise down the Na Pali Coast on a Kauai vacation and had incredible conditions. Because there was a hurricane just to the north the trade winds had stopped, so the boat could get closer than usual to the cliffs. Just as we were turning around a rainbow appeared just in front of the cliffs with the Kalalau Valley in the background. I used a polarizer to intensify the rainbow, and since I was shooting from a moving boat I had to up the ISO and shutter speed. Gear: Canon 5D MkIII, 24-105mm lens, ISO 500, 50mm, f14, 1/250 sec.