| 摘要 |
PURPOSE: To always stably and quickly control image magnification by forcibly changing a focal distance to either an upper limit focal distance or a lower limit focal distance. CONSTITUTION: The focal distance f0 of a variable power photographic lens is detected. Then, a distance x0 between a rear focus and a focusing position is detected based on the extending quantity of the focusing lens of the photographic lens and the focal distance f0. Besides, the image magnification of a photographing time is obtained based on the focal distance f0 and the distance x0. Next, a control focal distance is calculated based on the focal distance f0, the distance x0 and the image magnification. Further, the photographic lens is driven so as to make the focal distance coincide with the control focal distance. Then, when the control focal distance is out of the range between the upper limit focal distance and the lower limit focal distance of the photographing lens which can be changed, the photographic lens is driven so that the focal distance is forcibly changed to either the upper limit focal distance or the lower limit focal distance. |
