| 摘要 |
An image forming optical system, such as a photographic objective lens assembly is provided with a movable optical element. The movable optical element is designed and mounted so that it can optically interact with the transmission rays of the optical system or permit the rays to pass unaffected. The optical element can be a filter capable of improving the image forming characteristics of target object image to provide an advantageous soft focus, for example, as a portrait lens system or to provide a soft defocussed image. The optical filter element can have a central region capable of passing the converging or diverging transmitted rays through the optical system substantially free of refraction and a peripheral region capable of decreasing the transmitted image point intensity of rays transmitted therethrough. The optical filter element can be movable along the optical axis within a predetermined range of movement. This range of movement includes one position wherein the central region of the optical filter element will transmit all the incident rays. Various types of optical filters can be used such as filters with a peripheral region shaded to vary transmission intensity or given a refractive power.
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