The Photo Guide bills itself as the most comprehensive guide to photography on the App Store and I am inclined to agree. This US$4.99 app is a 250 MB download stuffed with information on all aspects of digital photography. The guide covers cameras, from point-and-shoot to DSLRs, with plenty of info on the capabilities of the cameras built into each iOS device. There's information on filters, composition, HDR photography, lighting, you name it.
Gallery: The Photo Guide
