Lens system for a copying machine

A three group, three component lens system comprising, in order from one side:

• a first, positive meniscus lens defining a convex surface directed to an object plane;
• a second, biconcave lens, and
• a third, biconvex lens,
• at least one of the three lenses being formed of plastic, the lens system included within a photocopier system having a fixed distance between the object plane and an image plane and requiring a clarity of image to correspond across an image having a fixed size in both the object and image planes, the lens system satisfying the following expressions:
• 40<0.5 (.nu..sub.1 +.nu..sub.3)<50 (a)
• where .nu..sub.1 is Abbe number of a material forming said first lens, and .nu..sub.3 is Abbe number of a material forming said third lens;
• 0.04f<f.sub.1 +f.sub.2 <0.20f (b)
• where f is a focal length of the entire lens system, f.sub.1 is a focal length of said first lens, and f.sub.2 is a focal length of said second lens;
• 0.05f<d.sub.4 <0.08f (c)
• where d.sub.4 is an axial distance between said second and third lenses, and
• 0.10<r.sub.4 /r.sub.5 <0.25 (d)
• where r.sub.4 is a radius of curvature of a surface of said second lens opposed to said third lens, and r.sub.5 is a radius of curvature of a surface of said third lens opposed to said second lens.

A three group, three component lens system comprising, in order from one side:

• a first, positive meniscus lens defining a convex surface directed to an object plane;
• a second lens having a negative power, and
• a third lens having a positive power,
• said second and third lenses being formed of plastic, and the lens system included within a photocopier system having a fixed distance between the object plane and an image plane and requiring a clarity of image to correspond across an image having a fixed size in both the object and image planes, the lens system satisfying the following expressions:
• 0.04f<f.sub.1 +f.sub.2 <0.06f (a)
• where f is a focal length of the lens system, f.sub.1 is a focal length of said first lens, and f.sub.2 is a focal length of said second lens;
• 0.015f<d.sub.2 <0.025f (b)
• where d.sub.2 is an axial distance between said first and second lenses;
• 0.05f<d.sub.4 <0.15f (c)
• where d.sub.4 ia an axial distance between said second and third lenses;
• 35<.nu..sub.1 <50, and (d)
• 1.65<N.sub.1
• where .nu..sub.1 is Abbe number of a material forming said first lens, and N.sub.1 is a refractive index at line d of the material forming said first lens.

A three group, three component lens system comprising, in order from one side:

• a first, positive meniscus lens defining a convex surface directed to an object plane;
• a second lens having a negative power, and
• a third lens having a positive power,
• said second and third lenses being formed of plastic, and the lens system included within a photocopier system having a fixed distance between the object plane and an image plane and requiring a clarity of image to correspond across an image having a fixed size in both the object and image planes, the lens system satisfying the following expressions:
• 0.015f<f.sub.1 +f.sub.2 <0.05f (a)
• where f is a focal length of the lens system, f.sub.1 is a focal length of said first lens, and f.sub.2 is a focal length of said second lens;
• 0.005f<d.sub.2 <0.015f (b)
• where d.sub.2 is an axial distance between said first and second lenses;
• 0.05f<d.sub.4 <0.15f (c)
• where d.sub.4 is an axial distance between said second and third lenses;
• 35<.nu..sub.1 <50, and (d)
• 1.65<N.sub.1
• where .nu..sub.1 is Abbe number of a material forming said first lens, and N.sub.1 is a refractive index at line d of the material forming said first lens.

A three group, three component lens system comprising, in order from one side:

• a first, positive meniscus lens defining a convex surface directed to an object plane;
• a second lens having a negative power, and
• a third lens having a positive power,
• said second and third lenses being formed of plastic, and the lens system included within a compact photocopier system having a fixed distance between the object plane and an image plane and requiring a clarity of image to correspond across an image having a fixed size in both the object and image planes, the lens system satisfying the following expressions:
• 0. 005f<d.sub.2 <0.025f (a)
• where f is a focal length of the lens system, and d.sub.2 is an axial distance between said first and second lenses;
• 0.05f<d.sub.4 <0.08f (b)
• where d.sub.4 is an axial distance between said second and third lenses;
• 35<.nu..sub.1 <50, and (c)
• 1.75<N.sub.1 <1.85
• where .nu..sub.1 is Abbe number of a material forming said first lens, and N.sub.1 is a refractive index at line d of the material forming said first lens;
• -0.1<r.sub.4 /r.sub.5 <0.25 (d)
• where r.sub.4 is a radius of curvature of a surface of said second lens opposed to said third lens, and r.sub.5 is a radius of curvature of a surface of said third lens opposed to said second lens.