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Method and apparatus for calibrating iris of photographic printer

  • US 5,767,950 A
  • Filed: 04/15/1996
  • Issued: 06/16/1998
  • Est. Priority Date: 04/15/1996
  • Status: Expired due to Fees
First Claim
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1. A method of calibrating an adjustable iris in a photographic printer including a light source, a sensor intended to produce a variable output in response to changes in an aperture of the iris, a lens system for projecting an image from a photographic negative illuminated by the light source, and an image plane where the projected image is received by a photographic paper, the iris being located in a light path from the light source so as to control an amount of light passing from the negative through the lens system to the paper, said method comprising steps of:

  • a) setting the iris at a reference aperture for a reference magnification of the lens system;

    b) near the image plane, measuring a reference intensity of light transmitted from the light source through the iris, in an absence of a photographic negative;

    c) calculating a modified intensity of light to be measured near the image plane after a predetermined change in stop number of the iris;

    d) changing the aperture of the iris in a direction to cause the intensity of light near the image plane to change from the reference intensity to the calculated modified intensity;

    e) during the changing, measuring the intensity of light near the image plane;

    f) stopping the changing of the aperture when the intensity measured near the image plane equals the calculated modified intensity;

    g) measuring an output Sv of the sensor when the intensity of light near the image plane equals the calculated modified intensity;

    h) repeating steps c) to g) for successive predetermined changes in stop number of the iris; and

    i) storing for use during operation of the photographic printer a correlation for each changed stop number among magnification settings of the lens system, the changed stop number and the output of the sensor at the changed stop number.

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