| 摘要 |
PURPOSE:To form a focus detecting device of simple, inexpensive constitution which has excellent responsiveness by comparing definition detected by a definition detecting means and detecting the focusing state of an image on an image pickup element. CONSTITUTION:The container 15 made of a ring-shaped piezoelectric element contracts in a right-left paper surface direction according to a voltage outputted by a voltage generating circuit 8 and elastic bodies 3 and 4 are pressed to deform to vary the shape of the elastic body 3 in an opening plate 5, so that a variable refracting power element 2 varies in refracting power and is controlled with a control signal theta supplied to the voltage generating circuit 8. Namely, when the refracting power of the variable refracting power element 2 increases, the image forming surface of a photographic optical system 1 moves to an object side and when the refracting power decreases, the surface moves to an image side. Consequently, detected sharpness values detected in at least two states wherein the refracting power of the variable refracting power element is different are compared to detect the focusing state of the image on the image pickup element. |
