| 摘要 |
An improved light-exposure control unit for a photographic printer offering minimized leakage problems, elimination of special precision capacitors and a range selecting circuit which eliminates masking of the photosensitive device used to detect variations in intensity of the light source. The improved control unit including operational amplifiers connected to the photosensitive device, which is mounted after the color filter but before the negative, sending a voltage adjustable according to the desired range and proportional to the amount of light impinging thereon, to an integrating amplifier with a variable input resistance adjusted accordingly to the desired density. The integrating amplifiers output is compared to a voltage derived from a precision reference source adjustable according to the settings made to magnification and speed-factor controls. The length of the exposure period is the time period required for the integrating amplifiers output to reach equality with this voltage and is controlled automatically by the amount of light impinging upon the photosensitive device, from the source, through the color filter.
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