| 摘要 |
PURPOSE:To surely attain a retrieval even to the variance of mark positions by visibly recognizing the position of a mark detecting unit on a screen. CONSTITUTION:A microfilm F has a frame 15 on which a picture is recorded and a mark 16 whose density is different from the margin added to the side edge of each frame. The frame 15 and the mark 16 on the film F are illuminat ed by a lamp 4 so as to project the picture on the frame on the screen 13 at the time of passing between glass plates 6 and 7. And the mark detecting unit 20 is constituted of a light emitting element 21 and a light receiving element 22 as a light source different from a lamp 4 which are oppositely equipped so as to put the film F between them. And by moving the mark detecting unit 20 in a direction shown with an arrow, the position of the mark detecting unit 20 can be read with a potentiometer 24. Thus, the position of the mark detecting unit can be visibly recognized on the screen and the accurate retrieval can be executed.
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