US 6,288,820 B1Granted

Image scanning lens having four lens elements and an image scanning unit that uses it

AssigneeFuji Photo Optical Co., Ltd.

InventorTakayuki Noda

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Abstract

An image scanning lens for an image scanner unit, such as a facsimile machine or document scanner is disclosed having only four lens elements with refractive power. In order from the object side, these are: a first lens element of positive refractive power and a meniscus shape with its convex surface on the object side; a second lens element of negative refractive power that is biconcave; a third lens element of positive refractive power that is biconvex; and a fourth lens element of negative refractive power having a concave surface on the object side. Various conditions are satisfied so as to provide a compact image scanning lens with a wide angle of view, and sufficiently corrected spherical aberration, astigmatism, and distortion so as to yield, when the lens is employed in an image scanner unit, a high quality scanned image that is comparatively bright.

Claims12

Dependent claims

An image scanning lens for a scanning unit, said image scanning lens formed of, in order from the object side, only four lens elements having refractive power as follows:

a first lens element of positive refractive power and meniscus shape having its convex surface on the object side;
a second lens element of negative refractive power that is biconcave;
a third lens element of positive refractive power that is biconvex;
and
a fourth lens element of negative refractive power having a concave surface on the object side;
wherein the following conditions are satisfied:
0.09≦DR3/f≦0.20
0.40≦|f4/f|≦1.30
ν4≧36.0
0.31≦ΣDi/f≦0.48
DR3-4/f≦0.07
where
DR3 is the on-axis thickness of the third lens element, in order from the object side;
f is the focal length of the image scanning lens;
f4 is the focal length of the fourth lens element, in order from the object side;
ν4 is the Abbe number of the fourth lens element, in order from the object side;
ΣDi is the overall length of the image scanning lens;
and
DR3-4 is the on-axis spacing between the third lens element and the fourth lens element, in order from the object side.

16 more elements

Dependencies are inferred from the claim text.