| 摘要 |
PURPOSE:To perform precise focusing detection while using light passed through a photographic lens efficiently by arranging a field lens near the focal plane of the photographic lens, and then providing two image forming lenses and a focusing detector across an optical axis and behind the field lens. CONSTITUTION:Luminous flux 100 arriving from a subject through a photographic lens is image-formed near a field lens 101 arranged near the focal plane. The light passes through the slit opening 102' of a mask 102 and the field lens 101 to reach two reflective optical systems 104 through a prism 103, and then passes said optical systems to be image-formed at points 1081 and 1082 on pnotoelectric converting elements 1071 and 1072 through a prism 105. Thus, a secondary image formation type optical system for focusing detection which is small- sized, uses luminous flux passed through the photographic lens effectively, and perform precise focusing detection even when the photographic lens is stopped down small is obtained. |
