| 摘要 |
In a copier which is capable of copying at a continuously variable magnification, light from a source 1 passes through a microfilm to be copied which is held by a scanning system 2, and is projected by a lens 3 onto a photosensitive drum 6 by way of a movable reflection system 4 and a fixed mirror 5. In order to measure the focal length f of the lens 3, the reflection system 4 is first positioned at a predetermined location and the lens 3 is moved until an image of optimum sharpness is obtained on the drum 6: the magnification M0 of this image is then measured. Following this, the reflection system 4 is moved a measured distance b to a position 4' to alter the optical path length between the microfilm and the drum 6 by DELTA I. The lens 3 is then moved to obtain a new image of optimum sharpness on the drum 6, whereupon the magnification M' of the new image is measured. The focal length f is then calculated by means of the formula: f = DELTA I/(1/M0 - 1/M' + M0 - M'). <IMAGE> |
