Browse Prior Art Database

CCTV Automatic Level Control

IP.com Disclosure Number: IPCOM000088321D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR

Abstract

This Closed Circuit Television (CCTV) arrangement maintains the depth of field of the optical system substantially constant as the light value on the image tube target is maintained substantially constant.

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CCTV Automatic Level Control

This Closed Circuit Television (CCTV) arrangement maintains the depth of field of the optical system substantially constant as the light value on the image tube target is maintained substantially constant.

The arrangement shown utilizes a rotatable neutral density linear wedge filter 10 to control the amount of light reaching the CCTV vidicon 12 but does not alter the effective aperture or "F" stop of the prime lens 14, so that the depth of field is constant. The sensing element or photocell 16 is located behind the prime lens 14 to encompass the prime lens field of view. This assembly is interposed between the prime lens and the imaging tube of a standard CCTV camera.

This automatic level control functions in the following manner: The (CCTV camera) lens 14 normally is adjusted to provide the optimum image on the target. A resistor 21 is adjusted to make the positive input of a comparator 31 positive with respect to the negative input.

A resistor 22 is adjusted to make the positive input of comparator 32 positive with respect to the negative input. This condition will provide positive outputs on both comparators 31, 32, and the wedge drive motor 34 will remain at rest.

An increase of light on the target of the vidicon 12 will lower the resistance of the photocell 16, which derives its light from the scene by way of a beam-splitting mirror 36. This will raise the voltage on the negative input of the comparator 31. When the negative inp...