def get_preview(self):
        """ Get a preview from the camera's viewport.

        This will usually be a JPEG image with the dimensions depending on
        the camera.  You will need to call the exit() method manually after
        you are done capturing a live preview.

        :return:    The preview image as a bytestring
        :rtype:     bytes
        """
        lib.gp_camera_capture_preview(self._cam, self.__camfile_p[0], self._ctx)
        lib.gp_file_get_data_and_size(self.__camfile_p[0], self.__data_p, self.__length_p)
        return ffi.buffer(self.__data_p[0], self.__length_p[0])[:]