Method and apparatus for calibrating iris of photographic printer
AssigneeEastman Kodak Company
InventorsJeffery Richard Hawver, Michael Joseph O'Brien, Andrea S. Rivers
Life of this patent
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Abstract
An adjustable iris diaphragm assembly (26) in a zoom lens system (16) of a photographic printer (10) is calibrated for each magnification setting by progressively adjusting the aperture opening until a predetermined light intensity is detected by a sensor (36) near a paper plane of the printer and then determining an output voltage of a feedback sensor (88) of the iris diaphragm assembly. A correlation is established among magnification settings of the printer, iris stop settings, and sensor output voltages to enable the printer to accurately set the iris for a desired exposure.
Claims14
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.
Apparatus for 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 apparatus comprising:
- a) means for setting the iris at a reference aperture for a reference magnification to of the lens system;
- b) means, near the image plane, for measuring a reference intensity of light transmitted from the light source through the iris, in an absence of a photographic negative;
- c) programmed computer means for calculating a modified intensity of light to be measured near the image plane after a predetermined change in stop number of the iris;
- d) means for 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) means for stopping the changing of the aperture when the intensity measured near the image plane equals the calculated modified intensity;
- f) means for measuring an output Sv of the sensor when the intensity of light near the image plane equals the calculated modified intensity;
- and
- g) means for storing for use during operation of 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.
Dependencies are inferred from the claim text.