Variable magnification slitwise exposure process and apparatus therefor for use with electrophotographic copying machine

Claim 1

A variable magnification slitwise exposure apparatus, for use with electrophotographic copying machines of the type in which a photosensitive surface is moved at a constant speed in a direction along a predetermined path having an exposure range therein at a fixed position while an original is scanned progressively by relative movement between the original and a source of light, said apparatus comprising: (a) holding means for supporting an original to be copied with its leading edge, considered in the scanning direction, always at a fixed position on the holding means irrespective of the magnification selected, (b) means operable to slitwise scan, at a constant rate which is adjusted dependent upon the magnification selected, an image of the original on said holding means, in order to transmit the original image onto said photosensitive surface, moving at said constant speed, at said fixed exposure range, (c) lens means having an optical axis and operable to focus the original image onto said photosensitive surface at said fixed exposure range, (d) means operable to adjust a first optical distance, between the original and said lens means, and a second optical distance, between saud lens means and said photosensitive surface, in accordance with the magnification selected, (e) means operable to adjust said lens means, in accordance with the selected magnification, in a direction perpendicular to the optical axis of said lens means at a magnification of unity, by a distance y which is expressed by the following equation: ##EQU8## wherein β represents the selected magnification and h represents the height of a portion of the original image being scanned at unity magnification, and (f) means maintaining constant the quantity of light incident on a unit of area of said photosensitive surface through said lens means at any magnification for a given original image.