В iOS 8 вроде предоставили доступ к этим параметрам
The AVFoundation framework makes it easier than ever for users to take great photos. Your app can take direct control over the camera focus, white balance, and exposure settings. Your app can also use bracketed exposure captures to automatically capture images with different exposure settings.
AV Foundation Framework Reference
Еще вот
тут можно посмотреть (обратите внимание на свойства и методы Available in iOS 8.0 and later. Ну и само собой на раздел Tasks)