FindBorders

// borders
private float _borderDown;
private float _borderLeft;
private float _borderUp;
private float _borderRight;

private void _FindBorders() {
    Camera cam = Camera.main; // cache camera
    // get world coordinates of four corners of screen
    Vector3 bottomLeft = cam.ScreenToWorldPoint(new Vector3(0, 0, Camera.main.transform.position.z * -1));
    Vector3 topRight = cam.ScreenToWorldPoint(new Vector3(Screen.width, Screen.height, cam.transform.position.z * -1));
    // get sides
    _borderDown = bottomLeft.y;
    _borderLeft = bottomLeft.x;
    _borderUp = topRight.y;
    _borderRight = topRight.x;
}