Retro-focus type wide angle objective lens

Claim 2

A retro-focus wide-angle objective lens corrected for short distance photography, comprising: a first lens group N at the object end and having a negative refractive power, a second lens group P closer to the image end and having a positive refractive power, said first lens group N including a front lens group having a negative refractive power and a rear lens group, said front lens group producing a divergent light bundle, said rear lens group being located in the divergent light bundle from the front lens group, said rear lens group having a negative lens toward the object end and a first positive lens, said second lens group P including a front positive lens facing said first positive lens of said rear lens group and a diaphragm disposed toward the image end of said front positive lens, said first and second lens groups N and P being movable toward the object for short distance photography, said front lens group and said second lens group P being movable in unison with each other at a rate different from the rate of said rear lens group.

Claim 3

A lens as in claim 1, wherein said front lens group of said first lens group N includes a negative lens adjacent said rear lens group.

Claim 4

A lens as in claim 2, wherein said rear lens group includes a negative meniscus lens concave to the image, said rear lens group having a biconvex lens with one surface more convex than a second surface, said one surface being directed toward the object end.

Claim 5

A lens as in claim 2, wherein said front lens group consists of a single negative meniscus lens concave to the image.

Claim 6

A lens as in claim 2, wherein said front lens group consists of two negative meniscus lenses concave to the image.

Claim 7

A retrofocus wide-angle objective lens corrected for short distance photography, comprising a pair of adjoining negative lenses with a first variable air space therebetween, a pair of adjoining positive lenses with a second variable air space therebetween, said negative lenses being disposed toward an object end and said positive lenses toward an image end of the objective lens, said lens toward the image end of said second variable air space forming at least a portion of a positive lens group having a positive refractive power, said lens toward the object end of said first variable air space forming at least a portion of a front lens group having a negative refractive power and said lenses between the variable air spaces forming a rear lens group, a diaphragm in said positive lens group disposed toward the image end of said positive lens facing the second variable air space, all of said lenses being movable toward the object for short distance photography, the rate of movement of said front lens group and said positive lens group being equal and in unison and being different from the rate of movement of said rear lens group.

Claim 8

A retrofocus wide-angle objective lens corrected for short distance photography, comprising a pair of adjoining negative lenses with a first variable air space therebetween, a pair of adjoining positive lenses with a second variable air space therebetween, said negative lenses being disposed toward an object end and said positive lenses toward an image end of the objective lens, said lens toward the image end of said second variable air space forming at least a portion of a positive lens group having a positive refractive power, said lens toward the object end of said first variable air space forming at least a portion of a front lens group having a negative refractive power and said lenses between the variable air spaces forming a rear lens group, a diaphragm in said positive lens group disposed toward the image end of said positive lens facing the second variable air space, all of said lenses being movable toward the object for short distance photography, the rate of movement of said front lens group and said positive lens group being equal and in unison and being different from the rate of movement of said rear lens group.

Claim 9

A lens as in claim 6, wherein said first variable air space is larger and said second variable air space is smaller during photography of an object at an infinite distance as compared with the air spaces during close-up photography.

Claim 10

A retrofocus wide-angle objective lens corrected for short distance photography, comprising: a first lens group and a second lens group and a third lens group in order from an object end to an image end, said first lens group having a divergent power, said second lens group including a negative group having at least one negative meniscus lens concave to the image, and one positive lens closer to the image end than the negative group, said third lens group having convergent power and having a positive lens toward the object end, a diaphragm incorporated into said third lens group closer to the image end than said front positive lens, means for moving the first and third lens groups and maintaining a constant space therebetween, means for moving the second lens group at a rate different from that of said first lens group during short distance photography.

Claim 11

A retrofocus wide-angle objective lens corrected for short distance photography, comprising: a first lens group and a second lens group and a third lens group in order from an object end to an image end, said first lens group having a divergent power, said second lens group including a negative group having at least one negative meniscus lens concave to the image, and one positive lens closer to the image end than the negative group, said third lens group having convergent power and having a positive lens toward the object end, a diaphragm incorporated into said third lens group closer to the image end than said front positive lens, means for moving the first and third lens groups and maintaining a constant space therebetween, means for moving the second lens group at a rate different from that of said first lens group during short distance photography.

Claim 12

A lens as in claim 8, wherein said first lens group has a negative lens adjacent to said second lens group.

Claim 13

A lens as in claim 9, wherein said one positive lens of said second lens group is a double convex lens having two convex surfaces, one convex surface being more convex than the other of the convex surfaces and facing the object end.

Claim 14

A lens as in claim 8, wherein said first lens group consists of a single negative meniscus lens concave to the image.

Claim 15

A lens as in claim 8, wherein said first lens group consists of two negative meniscus lenses concave to the image.