Are there any apps in the app store that work as a light meter? I have an old film camera that doesn't have a light meter, and it would be awesome if there were an app that I could put in an ISO and shutter speed and it gave me an aperture to get correct exposure. One app I found was Exposure Calc, but I didn't know if it was any good and didn't want to spend the money if it didn't even work. Anyone use it? Anyone know of a better app for what I want to do?