AnandTech - Manual Camera Controls in iOS 8
www.anandtech.com/show/8131/manual-camera-controls-in-ios-8
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
To be clear, iOS 8 will expose just about every manual camera control possible. This means that ISO, shutter speed, focus, white balance, and exposure bias can be manually set within a custom camera application. Outside of these manual controls, Apple has also added gray card functionality to bypass the auto white balance mechanism and both EV bracketing and shutter speed/ISO bracketing.