Refactored fast_autofocus

    def focus_rel(self, dz, backlash=False, **kwargs):

        self.keep_alive()

        # Start time and position

        self.stage_times.append(time.time())

        self.stage_positions.append(self.stage.position)

        # Main move

        self.stage.move_rel([0, 0, dz], backlash=backlash, **kwargs)

        # End time and position

        self.stage_times.append(time.time())

        self.stage_positions.append(self.stage.position)

        i = len(self.stage_positions) - 2

        return i, self.stage_positions[-1][2]

        # Index of the data for this movement

        data_index = len(self.stage_positions) - 2

        # Final z position after move

        final_z_position = self.stage_positions[-1][2]

        return data_index, final_z_position

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

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

    """Perform a down-up-down-up autofocus"""

    with microscope.camera.lock, microscope.stage.lock:

        with monitor_sharpness(microscope) as m:

            i, z = m.focus_rel(-dz / 2)

            # Move to (-dz / 2) 

            m.focus_rel(-dz / 2)

            # Move to dz while monitoring sharpness

            # i: Sharpness monitor index for this move

            # z: Final z position after move

            i, z = m.focus_rel(dz)

            # Get the z position with highest sharpness from the previous move (index i)

            fz = m.sharpest_z_on_move(i)

            i, z = m.focus_rel(-dz)  # move all the way to the start so it's consistent

            # Move all the way to the start so it's consistent

            # Store final absolute z position from this return move 

            i, z = m.focus_rel(-dz)  

            # Move to the target position fz

            # Can't do absolute move here yet so move by (fz - z)

            m.focus_rel(fz - z)

            # Return all focus data

            return m.data_dict()

    Run a fast autofocus

    """

    args = {"dz": fields.Int(missing=2000)}

    args = {"dz": fields.Int(missing=2000, example=2000)}

    def post(self, args):

        microscope = find_component("org.openflexure.microscope")

    """

    args = {

        "dz": fields.Int(missing=2000),

        "dz": fields.Int(missing=2000, example=2000),

        "backlash": fields.Int(missing=25, minimum=0),

    }