Although sunny-16 with negative film has a lot of leeway, I still like to have the assurance of a light meter. I carry an iPhone 5s, and there are quite a view light meter apps including one that claims to use matrix metering. I have compared the recommended settings with several of my metered cameras and they are nearly all within 1EV, which is usually fine with print film. I haven't used slide film for decades. Now if the phone only had a decent way to measure range for my guesstimate rangefinders. Anyone else have experience using cell phones as light meters?