Are you able to reproduce the auto-focus issue using the (non-Unity) Android VuforiaSamples 5.0.5 app?

SM-G850F with ISOCELL Sensor

Screenshot

Dimensions show - 1280 / 720 @ 30 fps

What is the model number of your Samsung Galaxy Alpha?

SM-G850[?]

Also, could you try the steps in this post and report what dimensions the Galaxy Alpha shows?

https://developer.vuforia.com/forum/android/lenovo-yoga-tablet-2-stretched-camera-no-2#comment-2051631

Asus Padfone - works fine

Motorola Nexus 6 - works fine

OnePlus One - works fine

NVidia Shield - works fine

Samsung Galaxy Note 4 - works fine

Now there is a problem only with Galaxy Alpha.

Back Camera:

focus-mode = auto

focus-mode-values = auto,infinity,macro,continuous-video,continuous-picture

Front Camera:

focus-mode = fixed

focus-mode-values = fixed,infinity

And as I wrote earlier - autofocus worked fine with the previous version of Vuforia. (4.2.3)

Can you try the following code (using Camera.Parameters) in a new Android Studio or Eclipse project to verify that your Samsung Galaxy Alpha supports continuous autofocus?

In the onResume():

Camera cam = Camera.open(0);
Camera.Parameters params = cam.getParameters();
List<String> focusModes = params.getSupportedFocusModes();

Add permission and features in AndroidManifest.xml:

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />

See also this post:

https://developer.vuforia.com/forum/vuforia-40/android-camera-continuous-autofocus-not-unsupported#comment-2050556

Are you able to reproduce this same behavior on any other Android devices?

Ok.

Far distance (~1000 mm.)

http://6.firepic.org/6/images/2015-08/01/0a1j5z628951.png

Middle distance

http://6.firepic.org/6/images/2015-08/01/tk7qf6b9rdl9.png

Near distance Vuforia 5 (~120 mm.)

http://2.firepic.org/2/images/2015-08/01/87v8gau2365x.png

http://2.firepic.org/2/images/2015-08/01/qgmowbkqcq8s.png

Near distance Vuforia 4.2.3 (~120 mm.)

http://2.firepic.org/2/images/2015-08/01/t7d4247xtklv.png

http://2.firepic.org/2/images/2015-08/01/plkdzx8qz64a.png

Can you specify what distance (roughly) you refer to with 'long range to medium' and with 'middle distance to nearest' ?

also, what is the size of the Target you are using ?

did you observe the same behaviour with the Image Targets sample ?

1. Check the Image Targets sample or the AR-VR sample 5.0.5; those implement continuous autofocus

2. Make sure you enable continuous autofocus after Vuforia starts; this is an example:

    void Start () 
    {
        VuforiaBehaviour.Instance.RegisterVuforiaStartedCallback(OnVuforiaStarted);
        VuforiaBehaviour.Instance.RegisterOnPauseCallback(OnPaused);
    }

    private void OnVuforiaStarted()
    {
        CameraDevice.Instance.SetFocusMode(
            CameraDevice.FocusMode.FOCUS_MODE_CONTINUOUSAUTO);
    }

    private void OnPaused(bool paused)
    {
        if (!paused) // resumed
        {
            // Set again autofocus mode when app is resumed
            CameraDevice.Instance.SetFocusMode(
                CameraDevice.FocusMode.FOCUS_MODE_CONTINUOUSAUTO);
        }
    }