| 摘要 |
PURPOSE:To put bodies at infinite-specific close distance in focus by moving a lens group on an optical axis relatively to an objective lens and a camera body. CONSTITUTION:Magnifying power of focal length is about 1.1-1.3 and relatively low and this is what is called RFC for a telephoto lens. This power allows focusing precision and a response speed to be maintained within sufficiently practical use ranges even when the RFC is mounted on a relatively dark telephoto lens with an about 2.8-3.5F number. Therefore, the composite back focus in infinite-distance focusing is made enough long even when the power is relatively low by selecting the value of object distance as the RFC properly. Further, advantages of aberration compensation are obtained because of the relatively low power, so the number of lens elements constituting the RFC is decreased and compact and simple constitution is obtained. |
