Abstract: A lens system for imaging includes, in order from the object side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, a stop, and a fourth lens group with positive refractive power. The third lens group includes, closest to the image plane side, a cemented lens on the object side of the stop and whose image plane-side surface includes a concave surface on the object side. The fourth lens group includes, closest to the object side, a cemented lens on the image plane side of the stop and whose object-side surface includes a concave surface on the image plane side. A radius of curvature g3er of the object side concave surface and the radius of curvature g4fr of the image plane side concave surface satisfy the following condition: 2.5?|g4fr/g3er|?4.0.

Abstract: There is provided a lens system composed, in order from an enlargement side, of a first lens group with positive refractive power and a second lens group with positive refractive power, wherein when zooming from a telephoto end to a wide-angle end, a distance between the first lens group and the second lens group decreases and a distance between the second lens group and a conjugate plane on a reduction side increases. The second lens group includes, closest to an enlargement side thereof, a lens with a second end surface that is concave on the enlargement side, and the first lens group includes a lens with an effective diameter of a first end surface closest to the reduction side that is larger than a maximum diameter in the second lens group.

Abstract: A lens system for imaging includes, in order from the object side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, a stop, and a fourth lens group with positive refractive power. The third lens group includes, closest to the image plane side, a cemented lens on the object side of the stop and whose image plane-side surface includes a concave surface on the object side. The fourth lens group includes, closest to the object side, a cemented lens on the image plane side of the stop and whose object-side surface includes a concave surface on the image plane side. A radius of curvature g3er of the object side concave surface and the radius of curvature g4fr of the image plane side concave surface satisfy the following condition: 2.5?|g4fr/g3er|?4.0.