| 摘要 |
PURPOSE:To find the quantity of movement of a focusing lens accurately and to perform speedy, high-accuracy focusing by providing an arithmetic means with a decision circuit which decides the defocusing direction of a photography system and an arithmetic circuit which performs arithmetic operation corresponding to the signal from the decision circuit. CONSTITUTION:The arithmetic means 3 is equipped with the decision circuit 4 which decides the direction of defocusing from a focus detecting means 2, a selecting circuit 5 which selects a specific characteristic signal among plural characteristic signals corresponding to sensitivity values characteristic to the photography system with the signal from the decision circuit 4, and the arithmetic circuit 6 which calculates the quantity of movement of the focusing lens 11 by utilizing the output signal of the focus detecting means 2 and the characteristic signal from the selecting circuit 5. Namely, when the quantity of movement of the focusing lens is found from the quantity of defocusing, the nonlinearity between the quantity of defocusing and the quantity of movement of the focusing is corrected, so the gradient of a curve is different with the direction of defocusing and then the decision circuit finds the direction of defocusing; and the selecting circuit selects a specific movement coefficient Sd among plural constants characteristic to the photography system 1 and the arithmetic circuit finds the quantity chi of the focusing lens from chi=DELTAd/Sd, where Sd is a movement coefficient and DELTAd is the quantity of defocusing. |
