There are plenty of fancy light meters on the market that help professional photographers get their exposure settings right. Thanks to Lightme for iPhone, you can turn your smartphone into a portable light meter with spot/average/zone/incident light metering. It supports multiple cameras and presets and offers frame previews for different focal lengths and formats.
This app has adjustable range of apertures and shutter speeds and supports reciprocity failure compensation for 20+ films. Lightme is available as a free download.[where to get it]