Sieve screen

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The screen diaphragm is an optical or photographic screen with several regularly or irregularly distributed openings. In contrast to the iris diaphragm , the use of the screen diaphragm does not selectively shade the rays near the edge from the bundle of rays, so that when optics with (practically unavoidable) residual defects are used, the imperfections during stopping down are retained or even increased. This is sometimes desirable, especially with portrait lenses, in which a sharp core image (from the rays near the optical axis ) is superimposed or outshone by a blurred edge ( bokeh ) ( soft focus ).

Examples

• Rodenstock Imagon lenses and lens heads with interchangeable, dimmable screen apertures (different focal lengths for different image formats)
• Fuji soft focus lenses with built-in screen apertures for various focal lengths and image formats
• Sima soft focus lens with interchangeable, but non-dimming screen diaphragms

Similar constructions

• Seibold's Dreamagon lens with slit segment diaphragm (4 / 90mm)