| 摘要 |
PURPOSE:To device the magnification of an objective automatically by providing a means which detects the quantity of Z-axial movement from the rising to the falling of a focusing point signal. CONSTITUTION:A sensor signal outputted from a subtracter 9 is divided by the output of an adder through a divider 22 to obtain a focusing signal DELTAS. The focusing signal DELTAS outputted by the divider 22 is compared by a comparator 24 with a threshold value Vref<->. Assuming that the distance from a focusing point is long when the focusing signal DELTAS is negative and too short when positive, the comparator 24 detects the threshold value Vref<-> twice (P1 and P2) if the distance to the focusing point decreases through the search operation of an automatic focusing mechanism. An objective decision device 26, therefore, decides the power of the objective 4 from the quantity DELTAZ of Z-axial movement from the point P1 to the point P2. Thus, the magnification of the objective 4 is decided automatically. |
