Projection device

#1. Field of the Invention

#This invention relates to a projection device of the slit scanning type such as, for example, a copying apparatus, and in particular to a projection device in which the magnification of a projected image can be varied.

#2. Description of the Prior Art

#FIG. 1 shows an embodiment of a copying apparatus to which a projection device according to the present invention is applied.

#FIGS. 2A and 2B show an embodiment of the imaging optical system of the projection device according to the present invention.

#FIG. 1 shows an embodiment of a copying apparatus to which the projection device of the present invention is applied. Reference numeral 1 designates a platen glass supporting an original thereon and movable in the direction of arrow A.sub.1, reference numeral 2 denotes a slit, reference numeral 3 designates a light source unit comprising a lamp and a reflector and illuminating the original, reference numeral 3' denotes an auxiliary reflecting mirror, reference numerals 4 and 6 designate mirrors for bending the optical path, and reference numeral 5 denotes a rotation-symmetrical main projection lens system which may be, for example, a variable magnification zoom lens and may be moved in the direction of arrow A.sub.2 during a magnification change. Reference numeral 7 designates a photosensitive drum, reference numerals 8 and 9 denote auxiliary lens systems each having an anamorphic imaging characteristic, and reference numeral 10 designates a housing for integrally holding the auxiliary lens systems. The housing 10 is movable in the direction of arrow A.sub.3 and by this movement, the auxiliary lens systems can be put into and out of the optical path. The housing 10 is of course so disposed that it does not intercept the optical path when the auxiliary lens systems 8, 9 are not present in the optical path.

#In a first condition, the auxiliary lens systems 8, 9 are disposed outside the optical path and the light flux from the original is projected onto the surface of the photosensitive drum by the main projection lens system 5. In this case, the main projection lens system 5 is a rotation-symmetrical system and therefore, the imaging magnifications in the lengthwise direction and the widthwise direction of the slit which are orthogonal to each other are equal to each other. In a second condition, the housing 10 is moved and the auxiliary lens systems 8, 9 are disposed on the optical path, and the light flux from the original is projected onto the surface of the photosensitive drum by the main projection lens system 5 and the auxiliary lens systems 8, 9. In this case, the imaging magnifications in the lengthwise direction and the widthwise direction of the slit differ from each other, but the original and the photosensitive drum are held optically conjugately in the two directions orthogonal to each other.

#An embodiment of the main projection lens system 5 and the auxiliary lens systems 8, 9 shown in FIG. 1 is shown in FIGS. 2A and 2B. FIG. 2A shows a cross-sectional view of the imaging system in the widthwise direction of the slit, and FIG. 2B shows a cross-sectional view of the imaging system in the lengthwise direction of the slit. The main projection lens system 5 is formed by a zoom lens which is of a symmetrical construction with respect to a stop S, and the lens data thereof will be shown below. In the table below, Ri represents the radius of curvature of the ith surface as counted from the original side, Di represents the on-axis thickness or the on-axis air space between the ith surface and the i+1th surface, .nu.d represents the Abbe number of each lens, and n represents the refractive index of each lens