| 摘要 |
PURPOSE:To improve the focusing accuracy and to shorten the focusing time, by producing the image forming position signal on the basis of the outputs of the 1st detecting means which detects the extent of shift of a distance control lens and the 2nd detecting means which detects the extent of shift of a variable magnification lens. CONSTITUTION:A 4-group zoom lens contains a distance control lens L11, a variable magnification lens L12 and a compensating lens L13, a master lens L14. The lens L11 contains a lens shift extent detecting means 1, and the lens L12 contains a lens shift extent detecting means 2 respectively. These means 1 and 2 include potentiometers, and the outputs of these potentiometers are connected to an arithmetic circuit 3. Then a resultant focal distance F2 and a primary point distance D are obtained from the output of the means 2, and DELTABF/DELTAD is obtained (DELTAD: shift extent of lens L11; DELTABF: shift extent of back focus to DELTAD). Thus the lens L11 is made dense and coarse by a focus detecting circuit when DELTABF/DELTAD is large and small respectively. |
