Reset tracker frames after each mode

            # Make timestamp absolute Unix time

            self.jpeg_times.append(frame.time)

            self.jpeg_sizes.append(frame.size)

        # Clear frame data for this move from the stream

        self.camera.stream.reset_tracking()

        # Index of the data for this movement

        data_index = len(self.stage_positions) - 2

        return data_index, final_z_position

    def move_data(self, istart, istop=None):

        "Extract sharpness as a function of (interpolated) z"

        """Extract sharpness as a function of (interpolated) z"""

        if istop is None:

            istop = istart + 2

        jpeg_times = np.array(self.jpeg_times)