Variable magnification type optical copier in which the copying size can be increased or decreased

Claim 2

In an optical copier of the type which is capable of both enlargement and reduction copying, said copier including a full speed mirror for scanning an original document, a zoom lens system consisting of only two relatively movable lens groups, said two relatively movable lens groups consisting of front and rear lens groups as viewed from the side of said original document, said zoom lens being movable along an optical path extending from said original document to a photo-sensitive drum for adjusting the magnification ratio of said copier, and half-speed mirrors disposed in said optical path between said full-speed mirror and zoom lens system and movable toward and away from said zoom lens system, the improvement characterized in that: the scanning moving region of said half-speed mirrors during unity and reduction magnification copying is overlapped with the moving region of said zoom lens system during enlargement copying; said front lens group has a positive focal length; and said rear lens group has a negative focal length.

Claim 3

The optical copier as claimed in claim 1, wherein said zoom lens system satisfies the following conditions: ##EQU10## where M max is the magnification of the high magnification side (enlargement side) of the magnification variation range, M min is the magnification of the low magnification side (reduction side) of the magnification variation range, M max /M min is the magnification variation ratio, f max is the focal length of the entire optical system in the unity magnification, f II is the focal length of the second lens group, ΔD I ,II is the amount of variation of the distance between the first and second lens groups, and r II P is the radius of curvature of the image side surface of the positive meniscus lens.

Claim 4

The optical copier as claimed in claim 2, wherein said zoom lens system is defined by: ##EQU11## ______________________________________ Lens Surface r d N ν ______________________________________ 1 60.078 7.49 1.69100 54.8 2 82.000 8.15 1.54072 47.2 3 41.500 4.56 4 64.838 10.62 1.65160 58.6 5 116.372 12.63 6 -106.775 6.41 1.62041 60.3 7 -56.405 3.64 8 -40.196 8.83 1.60342 38.0 9 -900.000 11.09 1.67790 55.3 10 -52.200 5.30˜21.41 11 -85.349 8.84 1.74950 35.3 12 -53.858 5.47 13 -52.200 5.00 1.78590 44.2 14 -112.397 ______________________________________ ##STR5## ##STR6## ##STR7## ##STR8## ______________________________________ where r represents the radius of curvature, d a lens thickness or an air distance between lenses along a d-line through the lens centers, N the refractive index of the lens material with respect to the d-line, ν the Abbe number of the lens material, f the focal distance of the entire zoom optical system, F.sub.∞ the F number with respect to an object at an infinite distance, M the magnification, ω the half view angle of the main beam, and NA the numerical aperture (NA=1/(2F.sub.∞ (1+|M|)).