DE4032051C2 - Long focal length lens - Google Patents

Description

The invention relates to a long focal length lens Features of the preamble of claim 1.

Long focal length lenses are especially for the Use with single-lens reflex cameras (SLR cameras) determined, with a high optical user Imaging performance and a relatively large image field be expected and focusing easily and quickly should be feasible.

High quality lenses in the medium telephoto range with large Opening ratio and large field of view are a. in the Japanese Patent Laid-Open 59-48723 and 63-205625 described.

Modern cameras are increasingly enabling autofocusing, what lenses with inner lens focusing were developed for where the focus is adjusted by just a few Lenses are made inside the lens. Such lenses are u. a. in Japanese Patent Laid-Open 1-154111 and 1-154112.

Japanese Patent Application Laid-Open 64-78208 and U.S. Patent No. 48 12 027 disclose a Gauss type lens in which a rear lens group is adjustable for focusing.  

However, if an inner lens is focusing on a Telephoto lens with a large aperture ratio and comparatively large image field is provided for the Adjustment of a movable one for focusing Lens group within the lens a larger free space necessary what the overall length of the lens in undesirable Way enlarged. In addition, the lens diameter be relatively large, so that marginal rays are still for imaging contribute significantly. This makes the lens bulky. in the In contrast, a lens of the Gauss type, in which for Focusing a rear lens group is adjusted Advantage of a relatively compact structure. On the other hand but the imaging performance is often lower, since the Adjustment of the lens group used for focusing considerable aberration changes can occur.

From DE 25 40 520 A1 it is known, in one of two Lens groups of existing long focal length lens Focusing only to move the rear lens group.

A long focal length lens of the type mentioned is known from DE 26 58 289 A1. Even if this is objective certain improvements in the correction of image errors, in particular the spherical aberration therefore not a sufficiently good image correction reached.

The invention has for its object a lens to create the type mentioned, in which the Image correction is further improved.

According to the invention, this object is achieved with the features of characterizing part of claim 1 solved.  

The solution according to the invention can advantageously be used for a comparatively compact lens construction and one comparatively large relative opening a high one Mapping performance can be achieved.

Further developments of the invention result from the Subclaims.

The long focal length lens according to the invention comprises

• - a front lens group of positive refractive power, which in the order from the item side at least two positive lenses, their object-side surfaces are strongly curved, and with a negative lens member a concave lens surface strongly curved on the image side has, and
• - a rear lens group of positive refractive power, the seen from the object side first lens surface is convex to the object, in which
• - to focus either only the rear lens group or the lens as a whole along the optical axis is adjustable
• - the rear lens group in the order of the At least one positive lens on the object side negative lens member with a concave on the image side Lens surface and at least one positive lens has and
• - the following conditions are met:
  0.5 <f / r _R1 <3.5, (1)
  0.6 <f _R / f <1.1 (2)
  and
  0.8 <f / r _R4 <3.0, (3)
  With
  f: focal length of the lens,
  f _R : focal length of the rear lens group,
  r _R1 : radius of curvature of the first lens surface of the rear lens group seen from the object side,
  r _R4 : radius of curvature of the image-side lens surface of the negative lens element of the rear lens group.

The following narrower condition is preferably also met in the lens according to the invention:

0.7 <f _R / f <1.0. (2 ')

A diaphragm can preferably be used in the lens according to the invention on the image side to the first lens surface of the rear lens group be arranged.

Fig. 13 of the drawings shows a sectional view of a lens according to the invention with a front lens group G _F and a rear lens group G _R in the basic structure. It can be seen from this that in the rear lens group G _R the lens surface S _r1 which is closest to the object is convex on the object side.

In contrast, in many conventional lenses in the rear lens group G _R, the lens surface S _r1 that is closest to the object is concave from the object view, as shown in FIG. 14 of the drawings.

In a conventional Gaussian lens, the aberrations that occur in the front and rear lens groups are compensated for in order to achieve good imaging performance, taking into account the symmetrical structure. When focusing by adjusting the rear lens group, however, the symmetrical structure is disturbed, which causes changes in the aberrations. In particular, the penetration height of an off-axis edge beam on the lens surface S _{R1 of} the rear lens group changes as a result of the focusing movement of the rear lens group G _R. As a result, the angle of incidence of this marginal ray changes on the concave lens surface S _R1 as a function of the adjustment movement of the rear lens group, as a result of which the aberrations can change considerably. During the focusing movement of the rear lens group of the objective from a setting at an infinite distance of the object to a setting at a short distance from the object, an asymmetry in terms of the imaging performance results.

On the other hand, in the lens according to the invention, the angle of incidence of an off-axis edge steel on the lens surface S _{R1 is} small due to its convex curvature, as shown in FIG. 13. Even with an adjustment of the rear lens group for lens focusing and thus with a change in the penetration height of this marginal ray on the lens surface S _R1 , the angle of incidence changes only relatively little, so that aberration changes resulting therefrom remain correspondingly low when focusing the lens at different distances from the object to be photographed .

The condition (1) relates to the radius of curvature r suitable _{R1 R1} for the lens surface S.

If this radius of curvature is extremely small, so that the upper limit of condition (1) is exceeded, the angle of incidence of an off-axis marginal ray on the lens surface S _{R1 of} the rear lens group changes when the lens is focused from a setting to an infinite object distance to a setting small object distance and with the resulting change in the penetration height of this beam so considerable that larger aberration changes and in particular larger changes in the coma occur.

If, on the other hand, the radius of curvature r _{R1 of} the lens surface S _{R1 of} the rear lens group is chosen to be so large that the lower limit of condition (1) is undershot, aberration changes which occur when the lens is focused can be kept small. However, it must be taken into account that condition (2) or (2 ') requires a sufficiently large positive refractive power of the rear lens group G _R. If the radius of curvature r _{R1 of} the lens surface S _{R1 of} the rear lens group were increased so much that the lower limit of condition (1) was undershot, the necessary refractive power of the rear lens group would have to be generated by the other lens members of this lens group, which would cause difficulties the compensation of image errors. In particular, it would be expected that negative spherical aberration would increasingly occur. It should also be noted that the rear lens group itself should be compact so that the adjustment space required for the focusing movement of the rear lens group remains ensured. Accordingly, the radius of curvature r _{R1 of} the lens surface S _{R1 of} the rear lens group must not be so large that the lower limit of condition (1) is undershot.

Conditions (2) and (2 ') describe the requirements placed on the converging refractive power of the rear lens group G _R.

Since the rear lens group G _{R is} adjusted to focus the lens, the lens must be equipped with the space required for the adjustment of this lens group. If the upper limit of condition (2) is exceeded, it becomes difficult due to the mechanical conditions to create such a large space that the lens can be focused even on small object distances. But even if a sufficiently large space for the adjustment of the rear lens group G _R can be created, this becomes objectively bulky. In the interest of the compactness of the lens and the possibility of focusing even on comparatively small object distances, the upper limit of condition (2) should not be exceeded. Preferably, even the upper limit of condition (2 ') should not be exceeded.

If the lower limit of the condition (2 ') or even the condition (2) is undershot, this serves to expand the focusing area to even smaller object distances and to further improve the compactness of the objective. However, there should be a certain minimum length of the rear focal length of the lens so that it can also be used in SLR cameras. Accordingly, there should also be a minimum value for the focal length f _{R of} the rear lens group, so that it is expedient not to fall below the lower limit of condition (2) and preferably also of condition (2 ').

Taking into account the conditions (1) and (2) or (2 '), the rear lens group G _R in combination with the front lens group G _F is intended to achieve a lens construction which allows aberrations to be effectively compensated for. In order to meet these requirements, it is desirable that the rear lens group G _R preferably has a triplet configuration or a modification thereof and that condition (3) is also fulfilled in order to further increase the functionality or the imaging performance.

Even if the radius of curvature r _{R1 of} the lens surface S _{R1 of} the rear lens group fulfills the condition (1), the converging refractive power of this lens surface can bring about a negative spherical aberration. It is therefore advantageous if the rear lens group G _{R is} equipped with a lens surface which compensates for this negative spherical aberration in order to ensure an advantageous overall effect of the rear lens group G _R , which is expressed by condition (3).

If the radius of curvature r _{R4 of} the image-side lens surface of a nagative lens element of the rear lens group G _{R is} so large that the lower limit of condition (3) is undershot, the negative spherical aberration generated by the lens surface S _{R1 of} the rear lens group remains. partially uncompensated.

On the other hand, if the radius of curvature r _{R4 of} the image-side lens surface of the nagative lens member of the rear lens group G _{R is} so small that the upper limit of condition (3) is exceeded, undesirable higher-order spherical aberrations occur.

Embodiments of a lens according to the invention longer Focal lengths are in the data tables below reproduced and are in terms of structure and Abberation curves explained in more detail using the drawings.

Show in the drawings

Fig. 1 is a sectional view of a lens according to an embodiment 1,

Fig. 2 1 (A) graphs of aberration curves of the lens of FIG. When focusing on the infinite object distance,

Fig. 2 (B) are graphs showing aberration curves of the lens of Figure 1 when focused on in accordance with a magnification ratio of 1:., 10

Fig. 3 is a sectional view of a lens according to an embodiment 2,

Fig. 4 (A) graphs of aberration curves of the lens of FIG. 3 in focusing on the infinite object distance,

FIG. 4 (B) are graphs showing aberration curves of the lens of Figure 3 in accordance with a focusing magnification ratio of 1:. 10,

Fig. 5 is a sectional view of a lens according to an embodiment 3,

Fig. 6 (A) graphs of aberration curves of the lens of FIG. 5 when focusing on the infinite object distance,

FIG. 6 (B) shows graphical representations of aberration curves of the objective according to FIG. 5 when focused according to an imaging scale of 1:10, FIG.

Fig. 7 is a sectional view of a lens according to an embodiment 4,

Fig. 8 (A) graphs of aberration curves of the lens of FIG. 7 by focusing on the infinite object distance,

Fig. 8 (B) are graphs showing aberration curves of the lens according to Fig 7 in accordance with a focusing magnification ratio of 1:. 10,

Fig. 9 is a sectional view of a lens according to an embodiment 5,

Fig. 10 (A) graphs of aberration curves of the lens of FIG. 9 when focused on the infinite object distance,

Fig. 10 (B) are graphs showing aberration curves of the lens shown in FIG 9 in accordance with a focusing magnification ratio of 1:., 10

Fig. 11 is a sectional view of a lens according to an embodiment 6,

Fig. 12 (A) graphs of aberration curves of the lens of FIG. 11 at infinite focus on the object distance,

FIG. 12 (B) shows graphical representations of aberration curves of the objective according to FIG. 11 when focusing according to an imaging scale of 1:10, FIG.

Fig. 13 is a sectional view of the basic structure of the lens according to the invention and

Fig. 14 is a sectional view of the basic structure of a conventional lens.

In the following data tables there is construction data Examples 1 to 6 of the lens according to the invention compiled.

Where:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between adjacent lenses,
n: refractive index of a lens for the d line,
ν: Abbe number of a lens and
f _B : rear focal length of the lens.

example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Claims (9)

1. Long focal length lens, comprehensive

• a) a front lens group (G _F ) of positive refractive power which, in order from the object side, has at least two positive lenses, the object-side surfaces of which are strongly convexly curved, and a negative lens element with a concave lens surface which is strongly curved on the image side, and
• b) a rear lens group (G _R ) of positive refractive power, the first lens surface (S _R1 ) of which, viewed from the object side, is convex to the object,
• c) the following condition is met:
  0.5 <f / r _R1 <3.5 (1)
  With
  f: focal length of the lens and
  r _R1 : radius of curvature of the first lens surface (S _R1 ) of the rear lens group (G _R ) seen from the object side,

characterized in that

• a) either only the rear lens group (G _R ) or the lens as a whole can be adjusted along the optical axis for focusing,
• b) the rear lens group (G _R ) has, in order from the object side, at least one positive lens, one negative lens member (L _Rn ) with a concave lens surface on the image side and at least one positive lens, and
• c) the following additional conditions are met:
  0.6 <f _R / f <1.1 (2)
  With
  f _R : focal length of the rear lens group (G _R ),
  and
  0.8 <f / r _R4 <3.0 (3)
  With
  r _R4 : radius of curvature of the image-side lens surface of the negative lens element (L _Rn ) of the rear lens group (G _R ).

2. Lens according to claim 1, characterized in that the following further condition is fulfilled:
0.7 <f _R / f <1.0 (2 ') 3. Lens according to claim 1 or 2, characterized in that an aperture on the image side to the first lens surface (S _R1 ) of the rear lens group (G _R ) is arranged. 4. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens. 5. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens. 6. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens. 7. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens. 8. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens. 9. Lens according to one of the preceding claims, characterized in that it has the data of the following table:
in which:
f: focal length of the lens,
ω: half the field of view of the lens,
r: radius of curvature of a lens surface,
d: thickness of a lens or air gap between neighboring lenses,
n: refractive index of a lens for the d line,
ν: Abbé number of a lens and
f _B : rear focal length of the lens.