protected void zoomCamera(float value) {
        distance = FastMath.clamp(distance + value, minDistance, maxDistance);
        camNode.setLocalTranslation(new Vector3f(0, 0, distance));
    }
move the camera toward or away the target

@param value the distance to move
jme3-core/src/main/java/com/jme3/app/ChaseCameraAppState.java