Как сфокусировать ближние объекты в iOS 8?

Я разрабатываю считыватель QR-кода. Мои коды имеют длину и ширину 1 см. Я использую метаданные AVFoundation для захвата машиночитаемых кодов, и все работает нормально. Но при этом мне нужно сфотографировать QR-код с логотипом (который находится посередине QR-кода). Поэтому я использую AVCaptureVideoDataOutput и didOutputSampleBuffer для получения неподвижных изображений. Проблема заключается в четкости изображения. он всегда выглядит размытым по краям кодов и логотипа. Поэтому я провел исследование ручного управления и внес некоторые изменения в код для ручной фокусировки, но до сих пор безуспешно.

1. Как сфокусировать (находящийся в 10см от камеры и крошечный) близлежащие объекты?
2. Есть ли у нас другой способ получить изображение после успешного сканирования из метаданных?
3. В чем разница между setFocusModeLockedWithLensPosition и focusPointOfInterest ?

Вот мой код (часть его)

   // Create and configure a capture session and start it running
- (void)setupCaptureSession
{
    NSError *error = nil;

    // Create the session
    _session = [[AVCaptureSession alloc] init];

    // Configure the session to produce lower resolution video frames, if your
    // processing algorithm can cope. We'll specify medium quality for the
    // chosen device.
    _session.sessionPreset = AVCaptureSessionPresetHigh;

    // Find a suitable AVCaptureDevice
    _device = [AVCaptureDevice
                               defaultDeviceWithMediaType:AVMediaTypeVideo];
    if ([_device lockForConfiguration:&error]) {
        [_device setAutoFocusRangeRestriction:AVCaptureAutoFocusRangeRestrictionNone];
        [_device setFocusModeLockedWithLensPosition:0.5 completionHandler:nil];
        //[device setFocusMode:AVCaptureFocusModeAutoFocus];
       // _device.focusPointOfInterest = CGPointMake(0.5,0.5);
       // device.videoZoomFactor = 1.0 + 10;
        [_device unlockForConfiguration];
    }

//    if ([_device isSmoothAutoFocusEnabled])
//    {
//        _device.smoothAutoFocusEnabled = NO;
//    }
    // Create a device input with the device and add it to the session.
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:_device
                                                                        error:&error];
    if (!input) {
        // Handling the error appropriately.
    }
    [_session addInput:input];

    // For scanning QR code
    AVCaptureMetadataOutput *metaDataOutput = [[AVCaptureMetadataOutput alloc] init];
    // Have to add the output before setting metadata types
    [_session addOutput:metaDataOutput];
    [metaDataOutput setMetadataObjectTypes:@[AVMetadataObjectTypeQRCode]];
    [metaDataOutput setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];

    //For saving the image to camera roll
    _stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
    [_stillImageOutput setOutputSettings:outputSettings];
    [_session addOutput:_stillImageOutput];

    // Create a VideoDataOutput and add it to the session
    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
    [_session addOutput:output];

    // Configure your output.
    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
    [output setSampleBufferDelegate:self queue:queue];

    // Specify the pixel format
    output.videoSettings =
    [NSDictionary dictionaryWithObject:
     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];


    // Start the session running to start the flow of data
    [self startCapturingWithSession:_session];

    // Assign session to an ivar.
    [self setSession:_session];
}

- (void)startCapturingWithSession: (AVCaptureSession *) captureSession
{
    NSLog(@"Adding video preview layer");
    [self setPreviewLayer:[[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession]];

    [self.previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];


    //----- DISPLAY THE PREVIEW LAYER -----
    //Display it full screen under out view controller existing controls
    NSLog(@"Display the preview layer");
    CGRect layerRect = [[[self view] layer] bounds];
    [self.previewLayer setBounds:layerRect];
    [self.previewLayer setPosition:CGPointMake(CGRectGetMidX(layerRect),
                                               CGRectGetMidY(layerRect))];
    [self.previewLayer setAffineTransform:CGAffineTransformMakeScale(3.5, 3.5)];

    //[[[self view] layer] addSublayer:[[self CaptureManager] self.previewLayer]];
    //We use this instead so it goes on a layer behind our UI controls (avoids us having to manually bring each control to the front):
    UIView *CameraView = [[UIView alloc] init];
    [[self view] addSubview:CameraView];
    [self.view sendSubviewToBack:CameraView];

    [[CameraView layer] addSublayer:self.previewLayer];


    //----- START THE CAPTURE SESSION RUNNING -----
    [captureSession startRunning];
    [self switchONFlashLight];
}

// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection
{
    // Create a UIImage from the sample buffer data
    [connection setVideoOrientation:AVCaptureVideoOrientationLandscapeLeft];
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
}
/ Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
{
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection{
    if (metadataObjects != nil && [metadataObjects count] > 0) {
        AVMetadataMachineReadableCodeObject *metadataObj = [metadataObjects objectAtIndex:0];
//        if ([_device lockForConfiguration:nil]){
//            [_device setAutoFocusRangeRestriction:AVCaptureAutoFocusRangeRestrictionNear];
//            _device.focusPointOfInterest = CGPointMake(metadataObj.bounds.origin.x, metadataObj.bounds.origin.y);
//            [_device unlockForConfiguration];
//        }

        if ([[metadataObj type] isEqualToString:AVMetadataObjectTypeQRCode]) {
            [_lblStatus performSelectorOnMainThread:@selector(setText:) withObject:[metadataObj stringValue] waitUntilDone:NO];
        }
    }    
}

Только для iOS 8 и последних iPhone.