enum {    AVCaptureDevicePositionBack = 1,    AVCaptureDevicePositionFront = 2};typedef NSInteger AVCaptureDevicePosition;

enum {    AVCaptureFlashModeOff = 0,    AVCaptureFlashModeOn = 1,    AVCaptureFlashModeAuto = 2};typedef NSInteger AVCaptureFlashMode;

enum {    AVCaptureTorchModelOff = 0,    AVCaptureTorchModelOn = 1,    AVCaptureTorchModeAuto = 2};typedef NSInteger AVCaptureTorchMode;

enum {    AVCaptureFocusModelLocked = 0,    AVCaptureFocusModeAutoFocus = 1,    AVCaptureFocusModeContinousAutoFocus = 2};typedef NSInteger AVCaptureFocusMode;

enum {    AVCaptureExposureModeLocked = 0,    AVCaptureExposureModeAutoExpose = 1,    AVCaptureExposureModeContinuousAutoExposure = 2};typedef NSInteger AVCaptureExposureMode;

enum {    AVCaptureWhiteBalanceModeLocked = 0,    AVCaptureWhiteBalanceModeAutoWhiteBalance = 1,    AVCaptureWhiteBalanceModeContinuousAutoWhiteBalance = 2};typedef NSInteger AVCaptureWhiteBalanceMode; 

AVCaptureDevice* d = nil; // find a device by position
NSArray* allDevices = [AVCaptureDevice devices]; 
for (AVCaptureDevice* currentDevice in allDevices) 
{   
       if (currentDevice.position == AVCaptureDevicePositionBack) 
       {     
               d = currentDevice;   
       } 
} 

// at this point, d may still be nil, assuming we found something we like.... 
NSError* err = nil; 
BOOL lockAcquired = [d lockForConfiguration:&err]; 
if (!lockAcquired) {    
       // log err and handle... 
} else {   
      // flip on the flash mode    
      if ([d hasFlash] && [d isFlashModeSupported:AVCaptureFlashModeOn] ) 
      {       
             [d setFlashMode:AVCaptureFlashModeOn];    
      }

    [d unlockForConfiguration]; 
}