Cannot lock focus with flash, iPhone 10

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Created Jan ’19

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Hi,

I'm having some issues locking the focus and taking a flash photo on iPhone 10 (iOS 12.0). I've made the simplest camera app I can that turns Flash on using a AVCapturePhotoSettings object, locks focus on the AVCaptureDevice using [device setFocusMode:AVCaptureFocusModeLocked]; and then takes a picture using capturePhotoWithSettings.

Regardless of the focus lock, auto focus still often happens, particularly when the preview is out of focus. Am I missing a settings, or a new way to lock focus? I have no issues on the iPhone 6 with this code.

This is essentially the full app (i have dropped most the error checking in this example, but no errors pop up):

// ViewController.h
//#import 
//@interface ViewController : UIViewController 
//@end

#import 
#import "ViewController.h"

@interface ViewController ()

@property (nonatomic) AVCaptureSession *session;
@property (nonatomic) AVCapturePhotoOutput *stillImageOutput;
@property (nonatomic) AVCaptureVideoPreviewLayer *videoPreviewLayer;

@property (weak, nonatomic) IBOutlet UIView *preview_view;
@property (weak, nonatomic) IBOutlet UIButton *take_picture_btn;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

-(void) viewDidAppear:(BOOL)animated
{
    self.session = [[AVCaptureSession alloc] init];
    self.session.sessionPreset = AVCaptureSessionPresetMedium;
    
    self.videoPreviewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.session];
    self.videoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspect;
    self.videoPreviewLayer.connection.videoOrientation = AVCaptureVideoOrientationPortrait;
    [self.preview_view.layer addSublayer:self.videoPreviewLayer];
    
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput* deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:NULL];
    [self.session addInput:deviceInput];
    
    self.stillImageOutput = [AVCapturePhotoOutput new];
    [self.session addOutput:self.stillImageOutput];

    [self.session commitConfiguration];
    
    dispatch_queue_t globalQueue =  dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
    dispatch_async(globalQueue, ^{
        [self.session startRunning];
        dispatch_async(dispatch_get_main_queue(), ^{
            self.videoPreviewLayer.frame = self.preview_view.bounds;
        });
    });
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [self.session stopRunning];
}

- (IBAction)take_picture:(id)sender {
    AVCapturePhotoSettings *settings = [AVCapturePhotoSettings photoSettings];
    settings.flashMode = AVCaptureFlashModeOn; // TURN ON FLASH
    AVCaptureDevice* device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    [device lockForConfiguration:nil];
    [device setFocusMode:AVCaptureFocusModeLocked]; // LOCK FOCUS
    [device unlockForConfiguration];
    [self.stillImageOutput capturePhotoWithSettings:settings delegate:self];
}

- (void)captureOutput:(AVCapturePhotoOutput *)output didFinishProcessingPhoto:(AVCapturePhoto *)photo error:(nullable NSError *)error {
    NSData *imageData = photo.fileDataRepresentation;
    if (imageData) {
        UIImage *image = [UIImage imageWithData:imageData];
        UIImageWriteToSavedPhotosAlbum(image,nil,nil,nil);
    }
}

@end

thanks for any help.

UDPATE: I've gone through Apples technical support. They have recognised this as a bug in the API on iPhone 8 and above. The auto-focus is not bypassed correctly when fixing the lens position. As of iOS 12.1.4 this is still an issue, but hopeful for a fix. No work around found as of yet.

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