My code was setting AVCaptureExposureModeCustom for AVCaptureDevicePositionBack however while adding support for iPhone 7 Plus I am able to set it for AVCaptureDeviceTypeBuiltInTelephotoCamera but not on AVCaptureDeviceTypeBuiltInDuoCamera.
What could be a possible solution to allow user set exposure for Duo Cam.
AVCaptureDeviceTypeBuiltInDuoCamera don't support RAW capture and manual controls. if you want to achieve manual control you have to select wide-angle or telephoto camera.
When you use the dual camera capture device, RAW capture and most manual controls are not available. To use these features, specifically select either the wide-angle or telephoto capture device.
Apple documentation link
The real reason why you cannot do manual controls is because duel camera device uses the system automatically chooses which camera to use during capture, and can combine data from both cameras to improve capture output.
Check iOSDeviceCompatibility for more info.
