def ray_shooting(self, theta_x, theta_y, kwargs_lens, k=None):
        """
        ray-tracing (backwards light cone)

        :param theta_x: angle in x-direction on the image
        :param theta_y: angle in y-direction on the image
        :param kwargs_lens:
        :return: angles in the source plane
        """
        x = np.zeros_like(theta_x)
        y = np.zeros_like(theta_y)
        alpha_x = theta_x
        alpha_y = theta_y
        i = -1
        for i, idex in enumerate(self._sorted_redshift_index):
            delta_T = self._T_ij_list[i]
            x, y = self._ray_step(x, y, alpha_x, alpha_y, delta_T)
            alpha_x, alpha_y = self._add_deflection(x, y, alpha_x, alpha_y, kwargs_lens, i)
        delta_T = self._T_ij_list[i+1]
        x, y = self._ray_step(x, y, alpha_x, alpha_y, delta_T)
        beta_x, beta_y = self._co_moving2angle_source(x, y)
        return beta_x, beta_y