| 摘要 |
PURPOSE:To simplify an optical system and a lens barrel by arranging an optical elastic body on the optical axis of a dichroic mirror on the object side and varying the refracting power of the optical elastic body in focus detection. CONSTITUTION:The optical elastic body 2 is, for example, a parallel plane body during photographing so that the photography is not affected much, and has one surface deformed so as to has positive refracting power during focus detection. Therefore, luminous flux from a light source 6 is reflected by the dichroic mirror 3a in an optical member 3 and then converged efficiently by the optical elastic body 2 while the F number is decreased, thereby projecting the light on an object side through the front group 1 of the optical system. Then, reflected luminous flux from the object side is guided by a photodetection lens 7 to the surface of a photodetecting element 8 and the position of the reflected luminous flux is measured on the surface of the photodetecting element 8 is measured to perform the focus detection. |
