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Illumination Compensation for Cos/4/ Theta Lens Attenuation

IP.com Disclosure Number: IPCOM000076699D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Hobgood, GW: AUTHOR

Abstract

A solution is proposed for Cos/4/ theta compensation for lens attenuation, when a well-focused illumination source is used for scanning. This is an alternative to the use of a slotted aperture for correcting the Cos/4/ theta attenuation.

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Illumination Compensation for Cos/4/ Theta Lens Attenuation

A solution is proposed for Cos/4/ theta compensation for lens attenuation, when a well-focused illumination source is used for scanning. This is an alternative to the use of a slotted aperture for correcting the Cos/4/ theta attenuation.

In copying machines, an aperture often referred to as a "dogbone" is used to control the uniformity of illumination at the photoconductor surface. Some copiers utilize tungsten lamps focused by an elliptical reflector onto the document to be copied. A thin line of light is projected onto the document as it is scanned. Due to the fact that the width of illumination is so narrow, a "dogbone" or aperture is not required to limit the width of image on the photoconductor. However, it is still necessary to correct for the Cos/4/ theta attenuation created by the lens. The narrowness of the illuminated width with a well-focused reflector makes correction difficult with an aperture. The proposed solution to this problem is to use a variable-density filter whose opacity varies as Cos/4/ theta, that is its attenuation varies as 1 over Cos/4/ theta to provide compensation for the lens loss. An example of such a filter is illustrated.

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