Patent Application
20140347743
1. Field of the Invention
The invention relates to a photographic wide-angle lens with internal focusing, comprising three lens arrays, namely a front array of negative refractive power that is rigid within itself and is fixed on the object-side, a rear array of positive refractive power that is rigid within itself and is fixed on the image side of an aperture diaphragm, and a focusing array of positive refractive power consisting of an optical single element that is arranged between the front array and the aperture diaphragm and is axially movable, the linear displacement of which from a maximum axial position on the object side to a maximum axial position on the image side allows to vary the focal distance from its maximum to its minimum value.
2. Description of the Related Art
Wide-angle lens systems of this type are known from U.S. Pat. No. 6,545,824 B2.
The known lens system comprises a front array that is configured in the traditional manner as a retrofocus array, having two negative meniscus lenses and one positive plano-convex lens. As is known, the retrofocus array essentially serves for shifting the focal plane of the lens system towards the back, i.e. towards the image-side, in order to design the rear vertex focal distance of the lens system larger than its focal length. This is particularly required with ultrawide-angle lens systems, to provide the necessary space for standardized connections of the lens system to a camera. On the image side of an aperture diaphragm, a rear array is arranged, which with the known lens system consists of a cemented biconvex and plano-concave lens element and of a non-cemented biconvex and plano-concave lens combination. For focusing, i.e. for adjusting the focus distance of the lens system, i.e. for adjusting the distance at which an object must be located in order to be imaged sharply in the detector plane of a connected camera, an optical single element is provided which is arranged between the front array and the aperture diaphragm which can be axially displaced. With the known lens system, this optical single element described here as focusing array is configured as a cemented component made up of a biconvex lens and a meniscus lens. As is known, the advantage of internal focusing is that on the one hand, instead of shifting the entirety of all arrays, only the focusing array with distinctly lower weight and correspondingly lower requirements for a motorized drive is moved, and on the other, the rear vertex focal distance does not change during focusing, and correspondingly none or only minor changes of the image scale occur. A problem with such internal focusing systems however is the correction of aberrations, since during focusing, the relative distances of the central lens range to the front array and the rear array, which are essential for correction, both change. For this reason, the resulting optical capacities are frequently limited. At an image field angle of below 90 degrees, the known lens system reaches merely a focal length of 35 mm at an f-number (ratio of the focal length to the diameter of the effective entrance pupil) of 3.6. The aberrations for the known lens system are stated to be a spherical aberration of up to 0.2%, an astigmatism of up to 0.3%, and a distortion of up to 3%.
A further lens system is known from US 2010/0265596 A1. This comprises a first lens cluster on the object side with a negative meniscus lens and a negative plano-concave lens. On the image side of the first lens cluster, a second lens cluster is arranged that consists of a third, fourth, fifth, sixth, seventh, eighth and ninth lens. The third, fifth, seventh and ninth lens are designed as biconvex lenses, the fourth and eighth lens, as negative meniscus lenses. The fifth and six, as well as the eighth and ninth lens, are each connected with a cemented component. A biconcave lens was used as the sixth lens. The known lens system does not have the ability of internal focusing.
The problem of the present invention is to develop a generic lens system such that an increased optical capacity is obtained, using a distinctly lower focal length.
This problem is solved by a photographic wide-angle lens system with internal focusing, comprising three lens arrays, namely, a front array of negative refractive power that is rigid within itself and is fixed on the object-side, a rear array of positive refractive power that is rigid within itself and is fixed on the image side of an aperture diaphragm and a focusing array of positive refractive power having an optical single element that is arranged between the front array and the aperture diaphragm and that is axially movable. Linear displacement of optical single element from a maximum axial position on the object side to a maximum axial position on the image side allows to vary the focus distance from its maximum to its minimum value. The optical single element of the focusing array comprises at least one aspheric surface and the end lens on the image side of the rear array is designed as a positive aspheric meniscus lens.
In this instance, the term “meniscus lens” refers to the basic form curved across the diameter of the lens in question and not necessarily to the equality of signs of the radii of curvature of the front and rear surface that always exists with spherical meniscus lenses. Because of the asphericity as taught by the invention, it is possible that the two surfaces may for example also be of biconvex shape locally, i.e. across a limited radial interval. The latter can be provided particularly for the central area of the end lens, which can extend over up to two thirds of the total diameter.
As a result of the aspheric configuration of the focusing array and in view of the mass of the array or the structural complexity of the array to be moved, it is possible to dispense with disadvantageous measures, such as the use of a cemented component. Instead, as provided in a preferred embodiment, it is possible to utilize a single lens, particularly a biconvex single lens, as focusing array. By the aspherization of at least one of the surfaces of the focusing array, it is possible to counteract the aberrations created in particular because of the principle of internal focusing. This will however require a compensating, likewise aspheric configuration of an element in the rear area of the lens system. For this purpose, the inventors selected the end lens of the rear array, i.e. the end element of the total lens system. A positive aspheric meniscus lens is provided specifically as end lens. This particular position is especially suitable for aspheric compensation. On the one hand, the distance between this correction lens and the detector plane of a connected camera, i.e. the rear vertex focal distance, is constant due to internal focusing, On the other, all of the aberrations introduced by the elements on the object side have totaled up to the axial position of the end lens and can be directly corrected prior to imaging in the image plane without further taking subsequent optical elements into consideration. As demonstrated further below by means of special embodiments of the invention, in this manner it is possible to achieve significantly improved optical capacity in terms of light intensity and error correction with significantly reduced focal length of the lens system. The particular advantage of the principle of internal focusing is preserved, however. In particular, the focusing array is located in the proximity of the aperture diaphragm, i.e. to the one axial position of the lens system where the beam of light has the smallest diameter. Consequently, the focusing array can also be configured with a corresponding small diameter. On the one hand, this has advantages in view of the mass to be moved during focusing; on the other, it facilitates the installation of a motorized drive, because of the smaller diameter of the focusing array, there is still sufficient installation space for a corresponding electric motor radially outside of the focusing array and still within the lens system housing, which is normally cylindrical.
In a preferred embodiment, it is provided that the front array comprises three immediately adjacent negative meniscus lenses with convex surfaces aligned on the object side. As a result of this, a high-quality retrofocus array can be realized which, as provided in a preferred embodiment, moreover has the structural advantage that all three meniscus lenses can be produced from the same type of glass.
The focusing array is arranged advantageously directly adjacent to the aperture diaphragm. As already previously mentioned, the advantage of this measure is that the focusing array is in the immediate proximity to the area of the smallest light beam diameter in the lens system. Accordingly, this will result in a very small minimum diameter of the focusing array, the consequence of which is a particularly large radial installation space for a motorized drive of the focusing array.
Alternatively to this, however, it can also be provided in another embodiment of the invention that a further lens element is arranged between the focusing array and the aperture diaphragm. Preferably, this is designed as a lens of negative refractive power, in particular a biconcave lens. This configuration will only slightly reduce the previously mentioned advantage with respect to the radial installation space, while permitting the creation of a somewhat enlarged axial installation space for the drive of the focusing array and/or for the diaphragm mechanism of the aperture diaphragm.
The rear array preferably is configured as a basic lens system that is capable of imaging. Normally, this is not corrected per se, however. The imaging is in principle essentially performed by means of this basic lens system. The axially preceding lenses serve to a lesser extent for imaging per se, but rather for the special modifications of the imaging, namely moving the focus back by the front array (retrofocus) and adjusting the focusing distance by the focusing array. The correction of aberrations is of course performed in view of all the aberrations that were introduced by all of the previously mentioned elements, so that the basic lens system is usually not corrected in itself.
The rear array, i.e. the basic lens system, in one configuration preferably comprises, from its object-side end to its image-side end, a lens of positive refractive power, a cemented component made up of a biconcave lens and a biconvex lens as well as the above-mentioned end lens designed according to the invention.
Further features and advantages of the invention result from the following specific description and the drawings.
a shows aspheric aberration,
a shows aspheric aberration,
a shows aspheric aberration,
a shows aspheric aberration,
a shows aspheric aberration,
a aspheric aberration,
Identical reference symbols in the figures indicate identical or analog elements.
In the embodiment shown, the focusing array II consists of a single lens with an object-side surface 51 and an image side surface 52, which is designated here as the fifth lens 5. The fifth lens 5 is designed as a biconvex lens, its objects-side surface 51 comprising a larger radius of curvature than its image-side surface. The fifth lens 5 is arranged so that it can be shifted axially, and is preferably motor-driven. It is arranged in the immediate proximity of the aperture diaphragm A. The fifth lens 5 is of aspheric design, both surfaces 51, 52 being preferably aspheric.
The rear array III comprises a sixth lens 6 with an object-side surface 61 and an image-side surface 62, a seventh lens 7 with an object-side 71 and an image-side surface 72, an eighth lens 8 with an object-side surface 81 and an image-side surface 82, as well as a ninth lens 9, with an object-side surface 91 and an image-side surface 92. The lenses 6, 7, 8, 9 of the rear array III are arranged in a reciprocally rigid manner as well as rigid in relation to the front array I and to the aperture diaphragm A. The sixth lens 6 is designed as a plano-convex lens, the object-side surface 61 of which is of curved design. The seventh lens 7 and the eighth lens 8 together forma cemented component, the seventh lens 7 being designed as a biconcave lens and the eighth lens 8 as a biconvex lens. The radius of curvature of the object-side surface 71 of the seventh lens 7 is smaller than the radius of curvature of its image-side surface 72. The radius of curvature of the image-side surface 81 of the eighth lens which is matched to the radius of curvature of the image-side surface 72 of the seventh lens is larger than the radius of curvature of its image-side surface 82. The ninth lens 9, as end lens of the lens system 100, is designed as a positive meniscus lens, the object-side surface 91 of which is of convex design. The ninth lens 9 is designed aspheric, both surfaces 91, 92 preferably being aspheric. Viewed across its entire diameter, the image-side surface 92 of the ninth lens 9 is of concave design; in its central area it is convex, however.
Because of the realized principle of internal focusing, the distance between the front array I and the rear array III and their distance from the image plane 200 is constant, whereas the distance of the fifth lens 5 of the focusing array II to the image plane 200 is variable. In particular, a displacement of the fifth lens 5 in direction of the front array I produces focusing of further distant objects on the image plane 200, and a displacement of the fifth lens 5 in direction of the aperture diaphragm A produces focusing of closer positioned objects on the image level 200.
A preferred concrete configuration of a lens system 100 according to
The aspheric shaped surfaces in the above Table 1 are marked with “asp.” This involves the two surfaces 51, 52 of the fifth lens of the focusing array II and the two surfaces 91, 92 of the end lens, i.e. the ninth lens 9. Here, the indicated negative radius of curvature of the image-side surface 92 refers to its central area. The aspheric coefficients are preferably as follows.
51: A=−0.763039E-05, B=−0.376225E-06, C=0.366786E-08
52: A=−0.180289E-04, B=−0.306385E-06, C=0.330624E-08
91: A=0.877599E-04, B=0.135798E-05, C=0.149129E-08
92: A=0.41240E-03, B=0.109228E-05, C=0.103390E-07
Because of the axial shiftability of the fifth lens 5, the distances of its surfaces 51, 52 change relative to the immediately adjacent surfaces when the focusing is adjusted. In particular, the distance between the fourth lens 4 and the fifth lens 5 varies between 0.75 mm for the “∞” setting and 3.5 mm for the setting to the minimum working distance, i.e. particularly 225 mm. The distance between the fifth lens 5 and the aperture diaphragm A varies correspondingly between 5.0 mm for the “∞” setting and 2.25 mm for the setting to the minimum working distance.
Such a lens system has a focal length between 14.45 mm (“∞” setting) and 13.4 mm (“minimum working distance” setting), an f-number between 2.11 (“∞”) and 2.07 (“minimum working distance”) and an aperture angle between 89.6° (“∞”) and 93° (“minimum working distance”).
The basic configuration of the embodiment of
Preferred values for the concrete configuration of a lens system of the embodiment according to
The aspheric shaped surfaces in the above Table 2 are marked with “asp.” This involves the two surfaces 51, 52 of the fifth lens 5 of the focusing array II, the object-side surface 61 of the sixth lens 6 and the two surfaces 91, 92 of the end lens, i.e. the ninth lens 9. Here, the stated negative radius of curvature of the image-side surface 92 refers to its central area. The aspheric coefficients are preferably as follows.
51: A=−1.63452E-05, B=−0.659234E-07, C=−0.108755E-09
52: A=0.494587E-05, B=−0.748355E-07, 0=0.118988E-09
61: A=−0.179157E-04, B=-0.887314E-07, C=0.252232E-09
91: A=0.139413E-03, B=0.103833E-05, C=0.118247E-08
92: A=0.176934E-03, B=0.102411 E-05; C=0.486927E-08
Because of the axial shiftability of the fifth lens 5, the distances of its surfaces 51, 52 change relative to the immediately adjacent surfaces when the focusing is adjusted.
In particular, the distance between the third lens 3 and the fifth lens 5 varies between 24.7 mm for the “∞” setting and 27.45 mm for the setting to the minimum working distance, namely particularly 225 mm. The distance between the fifth lens 5 and the aperture diaphragm A varies correspondingly between 5.0 mm for the “∞” setting and 2.25 mm for the setting to the minimum working distance.
Such a lens system 100′ has a focal length between 14.46 mm (“””) and 13.06 mm (“minimum working distance”), an f-number between 2.11 (“∞”) and 2.08 (“minimum working distance”) and an aperture angle between 89.6° (“∞”) and 94.6° (“minimum working distance”).
The basic configuration of the lens system 100″ according to
Preferred values for the concrete configuration of a lens system according to
The aspheric shaped surfaces are marked with “asp” in the above Table 3. This involves the image-side surface 52 of the fifth lens 5 of the focusing array II and the two surfaces 91, 92 of the end lens, i.e. the ninth lens 9. Here, the stated “plane” radius of curvature of the image-side surface 92 refers to its central area. The aspheric coefficients are preferably as follows.
f52: A=−0.282076E-04, B=−0.348231E-07, C=−0.128230E-09
f91: A=0.697625E-04, B=0.719545E-06, C=0.484016E-08
f92: A=0.137339E-03, B=0.469719E-06, C=0.115923E-0
Because of the axial shiftability of the fifth lens 5, the distances of its surfaces 51, 52 change relative to the immediately adjacent surfaces when the focusing is adjusted. In particular, the distance between the fourth lens 4 and the fifth lens 5 varies between 0.75 mm for the “∞” setting and 3.5 mm for the setting to the minimum working distance, namely particularly 225 mm. The distance between the fifth lens 5 and the tenth lens 10 accordingly varies between 3.5 mm for the “∞” setting and 0.75 mm for the setting to the minimum working distance.
Such a lens system 100″ has a focal length between 14.45 mm (“∞”) and 13.38 mm (“minimum working distance”), an f-number between 2.11 (“∞”) and 2.08 (“minimum working distance”) and a viewing angle between 89.6° (“∞”) and 93.2° (“minimum working distance”).
The embodiments discussed in the specific description and shown in the Figures obviously represent merely illustrative embodiments of the present invention.
In the light of the present disclosure a person skilled in the art has a broad spectrum of optional variations available.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 105 425.0 | May 2013 | DE | national |
