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Auto-focusing apparatus

  • US 5,512,951 A
  • Filed: 01/11/1995
  • Issued: 04/30/1996
  • Est. Priority Date: 06/02/1992
  • Status: Expired due to Term
First Claim
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1. An auto-focusing apparatus which obtains an evaluation value from a contrast component of a video signal representing an image on a screen, and which performs a focus adjustment of a focus lens so that the evaluation value will be at a at a maximum value, comprising:

  • measurement frame setting means for setting a first frame and a second frame which are substantially centered at the center of said screen with said second frame being smaller than said first frame;

    evaluation value generating means for obtaining a first evaluation value and a second evaluation value from a first position in said first frame and from a second position in said second frame, respectively;

    means for detecting whether said second evaluation value is generated;

    means responsive to the absence of said second evaluation value for setting a third frame, wherein said third frame is offset from the center of said screen and excludes a portion of the screen surrounding said first position for which said first evaluation value is based, and for generating a third evaluation value from said third frame;

    means also responsive to the absence of said second evaluation value for selecting either said first evaluation value or said third evaluation value whichever is based on a position nearer to the center of said screen; and

    means for effecting said focus adjustment based on said second evaluation value when detected or, in the absence of said second evaluation value, based on the selected first or third evaluation value.

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