I took my first waterfall pictures just recently so technically can't add informed choice. Just a couple thoughts- I love using a tilt shift lens whenever I can- But my experience with the waterfalls was I got wet, camera got wet, lens got wet... and the Tilt shifts are the least environmentally sealed lenses available, I'd be worried about it. If you are looking into renting anyway... what about renting the required filter for your rokinon?