I have no issues with folks using an iPhone app to preview before they shoot. In fact, I might buy an outdated DSLR with a decent LCD screen and some cheap lenses for this purpose. I'd consider using an iPhone except; 1. I don't have or need an iPhone and, 2. I'll be shooting ultra-wide sometimes (wider than iPhones can capture). What's stopping me from getting a DSLR and lenses is cost. I did purchase a used director's viewfinder with a wide-angle adapter and this combo will get close enough to the same viewing angles and aspect ratios I intend to shoot... close enough that I can interpolate from what it shows me.