| 摘要 |
PURPOSE:To prevent a focus variation due to various causes by moving other lens group than a variable power lens group in a zoom lens in accordance with a signal generated by three detecting means corresponding to each of a variation of temperature and humidity, a variation of a distance of an object to be photographed, and a variation of a focal distance caused by a variable power. CONSTITUTION:A zoom lens is provided with a focal distance detecting mechanism 6 for generating an electric signal showing a focal distance of the zoom lens from a moving extent of the second lens group 2 for a variable power, a temperature and humidity detecting mechanism 7 for generating an electric signal corresponding to temperature and humidity, and a photographed object distance detecting means 8 for generating an electric signal showing a distance of an object to be photographed. These three electric signals are inputted and the operation is executed by a focusing member moving extent calculating mechanism 9, by which an electric signal showing a necessary moving extent of the third lens group for not generating a focus variation as the zoom lens even if a variation of three catagories is generated is outputted. An output electric signal of this calculating mechanism 9 is applied to a focusing member driving mechanism 10, and the third lens group 3 being a focusing member is moved along the optical axis. |
