I just buy a great iPhone app, lens gallery, I like iPhone, and I like photography too. But it’s not easy for me to choose a SLR lens. with this tools, I find many excellent photos, at first, I want give up my canon 17-85 EF-IS lens, but when I search photo in Lens Gallery, I find many great photo that taken by this lens, I understand lens only is a tool, the most important things is you must think and think before you shoot.
You can find it out by follow this link in Apple iTunes App Store. good luck. :D