Lens having a fixed focal length and constant overall length for auto focus applications including five lens groups of ++--+, -++-+, -+++-, -++--, +-+--, +-++- or ++++- refractive powers

Abstract

A lens system with a fixed focal length includes five lens groups. The five lens groups include a first lens group, a second lens group configured as a focusing front group, a third lens group having a negative refractive power, a fourth lens group configured as a focusing back group, and a fifth lens group. The fifth lens group has a positive refractive power that is arranged in a stationary manner relative to an imaging plane in a lens barrel and both the focusing front group and the focusing back group are movable jointly relative to one another and to the lens groups arranged in a stationary manner in order to focus the fixed focus length lens system on objects at different object distances.

Claims

1. A lens system with a fixed focal length, comprising: five lens groups, wherein three lens groups are mounted in a stationary manner and two lens groups are mounted in a displaceable manner along an optical axis, wherein the lens system comprises the following lens groups in order from an object side of the lens system to an image side: a first lens group, as viewed from an object side, that is arranged in a stationary manner having a positive refractive power, a second lens group configured as a focusing front group that is arranged in a displaceable manner, a third lens group having a negative refractive power and containing a stationary iris diaphragm, an aperture of which is adjustable, the third lens group being arranged in a stationary manner, a fourth lens group configured as a focusing back group that is arranged in a displaceable manner, and a fifth lens group having a positive refractive power that is arranged in a stationary manner relative to an imaging plane in a lens barrel and both the focusing front group and the focusing back group are movable jointly relative to one another and to the lens groups arranged in a stationary manner in order to focus the fixed focus length lens system on objects at different object distances.

2. The lens system as claimed in claim 1, wherein the focusing front group has a positive refractive power and the focusing back group has a negative refractive power.

3. The lens system as claimed in claim 1, wherein the focusing front group has a positive refractive power and the focusing back group has a negative refractive power, and the focusing front group moves away from the imaging plane during focusing from infinity to the near setting and the focusing back group moves toward the imaging plane during focusing from infinity to the near setting.

4. The lens system as claimed in claim 1, wherein a) the ratio f1/f of the focal lengths f1 of the front lens group and f of the entire lens lies between 40 and 30, b) the ratio f2/f of the focal lengths f2 of the focusing front group and f of the entire lens lies between 10 and 20, c) the ratio f3/f of the focal lengths f3 of the third group and f of the entire lens lies between 30 and 40, d) the ratio f4/f of the focal lengths f4 of the focusing back group and f of the entire lens lies between 10 and 20, and e) the ratio f5/f of the focal lengths f5 of the fifth lens group and f of the entire lens lies between 40 and 30.

5. The lens system as claimed in claim 1, wherein the lens has a ratio of the total focal length f to the image circle diameter in the imaging plane of between 0.3 and 5.

6. The lens system as claimed in claim 1, wherein the ratio V of the volume of the respective focusing elements to the image circle diameter in the imaging plane raised to the third power lies below 0.1 (V/Bd.sup.3<0.1), in particular below 0.08, or the weight of the respective focusing group lies below 15 g (grams).

7. The lens system as claimed in claim 1, wherein the front lens group consists of three lens elements, wherein the first lens element and the second lens element have a negative refractive power and the third lens element has a positive refractive power, wherein the second lens element and the third lens element are combined to form a lens doublet having a negative total refractive power.

8. The lens system as claimed in claim 1, the third group consists of two lens elements, wherein a first lens element has a negative refractive power and a second lens element has a positive refractive power, and the iris diaphragm is arranged in a stationary fashion between the first lens element and the second lens element.

9. The lens system as claimed in claim 1, the fifth lens group consists of two lens elements, wherein a first lens element has a positive refractive power and a second lens element has a negative refractive power.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In this case, in the figures:

(2) FIG. 1 shows a lens-element section through a lens with the focal length 90 mm and the maximum aperture number 2,

(3) FIG. 2 shows a lens-element section through a lens with the focal length 75 mm and the maximum aperture number 2,

(4) FIGS. 3 and 5 show a lens-element section through in each case a lens with the focal length 24 mm and the maximum aperture number 2,

(5) FIG. 4 shows a lens-element section through a lens with the focal length 50 mm and the maximum aperture number 2,

(6) FIGS. 6 and 7 show a lens-element section through a lens with the focal length 90 mm and the maximum aperture number 2,

(7) FIGS. 8 and 9 show a lens-element section through in each case a lens with the focal length 50 mm and the maximum aperture number 1.4,

(8) FIG. 10 show an image sensor in an imaging plane IM.

DETAILED DESCRIPTION

(9) The movement paths of the respective lens-element groups during the focusing process are illustrated below the lens-element sections in the figures. Horizontal lines represent the positions of the lens-element groups G1, G2, G3, G4 and G5. The upper lines thereof identify the positions in the focus setting infinity, the lower lines the positions in the focus setting at the shortest object distance, and the central lines the positions in a central focus setting. The perpendicular lines are assigned to the stationary lens-element groups G1, G3 and G5, and the oblique lines to the displaceable focusing groups G2 and G4.

(10) The lens-element sections in the drawing are illustrated to scale, such that relative indications, such as e.g. the material thickness in the case of the lens element G5L2 in FIG. 1, which is considerably thinner in the lens-element center in comparison with the material thickness at the lens-element edge, can be diagrammatically established and checked using conventional geometric means. What is likewise disclosed in this way is that in FIG. 1 the lens element G1L2 has in the lens-element center a material thickness almost exactly two times (2.11 times) thicker than the lens element G1L1. These relationships are readily apparent to the person skilled in the art and so lens-geometries can also be inferred. By way of example, FIG. 1 illustrates that the first lens-element group G1 as viewed from the object side is constructed from, in an order as viewed in the light direction to the imaging plane IM, two convexo-concave lens elements having a positive refractive power, which are spaced apart by approximately the thickness of the first lens element G1L1 and are assigned downstream at a smaller distance a cemented element consisting of a biconvex lens element having a positive refractive power and a biconcave lens element having a negative refractive power.

(11) Concrete exemplary embodiments are evident from the tables below for lenses with a focal length of 90 mm, 70 mm, 50 mm and 24 mm with a maximum aperture number of 2 and two lenses with a focal length of 50 mm and a maximum aperture number of 1.4, wherein the focal lengths are in each case relative to the full-frame format (43.3 mm image circle diameter).

(12) TABLE-US-00001 FIG. 1 Focal length Refractive 2/90 f [mm] power [Dpt.] fGr/f Construction G1 176.5 5.7 2.0 + G2 55.0 18.2 0.6 + G3 91.0 11.0 1.0 G4 90.4 11.1 1.0 G5 72.1 13.9 0.8 +

(13) TABLE-US-00002 FIG. 2 Focal length Refractive 2/75 f [mm] power [Dpt.] fGr/f Construction G1 159.1 6.3 2.1 + G2 55.0 18.2 0.7 + G3 91.0 11.0 1.2 G4 96.1 10.4 1.3 G5 72.1 13.9 1.0 +

(14) TABLE-US-00003 FIG. 3 Focal length Refractive 2/24 f [mm] power [Dpt.] fGr/f Construction G1 36.5 27.4 1.5 G2 133.2 7.5 5.6 + G3 18.0 55.6 0.8 + G4 24.9 40.2 1.0 G5 125.6 8.0 5.2 +

(15) TABLE-US-00004 FIG. 4 Focal length Refractive 2/50 f [mm] power [Dpt.] fGr/f Construction G1 83.9 11.9 1.7 G2 63.0 15.9 1.3 + G3 29.9 33.5 0.6 + G4 66.1 15.1 1.3 G5 84.8 11.8 1.7

(16) TABLE-US-00005 FIG. 5 Focal length Refractive 2/24 f [mm] power [Dpt.] fGr/f Construction G1 37.6 26.6 1.6 G2 105.1 9.5 4.4 + G3 18.4 54.3 0.8 + G4 42.4 23.6 1.8 G5 499.2 2.0 20.8

(17) TABLE-US-00006 FIG. 6 Focal length Refractive 2/90 f [mm] power [Dpt.] fGr/f Construction G1 64.9 15.4 0.7 + G2 61.3 16.3 0.7 G3 32.4 30.9 0.4 + G4 76.5 13.1 0.8 G5 111.2 9.0 1.2

(18) TABLE-US-00007 FIG. 7 Focal length Refractive 2/90 f [mm] power [Dpt.] fGr/f Construction G1 53.1 18.8 0.6 + G2 36.4 27.5 0.4 G3 78.8 12.7 0.9 + G4 79.8 12.5 0.9 + G5 68.0 14.7 0.8

(19) TABLE-US-00008 FIG. 8 Focal length Refractive 1.4/50 f [mm] power [Dpt.] fGr/f Construction G1 80.9 12.4 1.6 + G2 78.5 12.7 1.6 G3 56.7 17.6 1.1 + G4 108.4 9.2 2.2 + G5 87.9 11.4 1.8

(20) TABLE-US-00009 FIG. 9 Focal length Refractive 1.4/50 f [mm] power [Dpt.] fGr/f Construction G1 581.0 1.7 11.6 + G2 95.1 10.5 1.9 + G3 62.5 16.0 1.3 + G4 106.3 9.4 2.1 + G5 104.3 9.6 2.1