How to get autofocus working with CameraSource from Android's Mobile Vision API?

Question

I'm trying get the Camera to autofocus using the CameraSource class from Android Mobile Vision API.

I've activated autofocus as follows:

cameraSource = new CameraSource
                .Builder(this, barcodeDetector)
                .setRequestedPreviewSize(640, 480)
                .setAutoFocusEnabled(true)
                .setRequestedFps(24.0f)
                .build();

But the SurfaceView rendering the camera is often blurred.

Here my full Activity's code:

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.util.Log;
import android.util.SparseArray;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;

import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.barcode.Barcode;
import com.google.android.gms.vision.barcode.BarcodeDetector;

import java.io.IOException;
import java.util.Arrays;

public class MainActivity extends Activity {

    private BarcodeDetector barcodeDetector;
    private CameraSource cameraSource;
    private SurfaceView cameraView;
    private TextView barcodeInfo;

    public static int REQUEST_PERMISSION_CAMERA = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        cameraView = (SurfaceView) findViewById(R.id.camera_view);
        barcodeInfo = (TextView) findViewById(R.id.code_info);

        barcodeDetector =
                new BarcodeDetector.Builder(this)
                        .setBarcodeFormats(Barcode.QR_CODE)
                        .build();

        cameraSource = new CameraSource
                .Builder(this, barcodeDetector)
                .setRequestedPreviewSize(640, 480)
                .setAutoFocusEnabled(true)
                .setRequestedFps(24.0f)
                .build();

        cameraView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                try {

                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                        if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                            requestPermissions(new String[]{Manifest.permission.CAMERA}, REQUEST_PERMISSION_CAMERA);
                            return;
                        } else {
                            cameraSource.start(cameraView.getHolder());
                        }
                    } else {
                        cameraSource.start(cameraView.getHolder());
                    }
                } catch (IOException ie) {
                    Log.e("CAMERA SOURCE", ie.getMessage());
                }
            }

            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                cameraSource.stop();
            }
        });

        barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
            @Override
            public void release() {
            }

            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> barcodes = detections.getDetectedItems();

                if (barcodes.size() != 0) {
                    barcodeInfo.post(new Runnable() {    // Use the post method of the TextView
                        public void run() {
                            barcodeInfo.setText(    // Update the TextView
                                    barcodes.valueAt(0).displayValue
                            );
                        }
                    });
                }
            }
        });

    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        int[] checkValues = new int[1];
        if (requestCode == REQUEST_PERMISSION_CAMERA) {
            if (Arrays.equals(grantResults, checkValues)) {
                if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                    return;
                }
                try {
                    cameraSource.start(cameraView.getHolder());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraSource.release();
        barcodeDetector.release();
    }
}