Anamorphic optical system, image pickup device, on-board type camera and monitoring camera

The present invention relates to a lens optical system of an on-board type camera (a camera carried on board of a vehicle), mounted on front and rear side or on lateral side of a moving object such as an automobile, or to a lens optical system of a monitoring camera for taking and recording images inside or outside of a vehicle while a moving object such as an automobile is being driven or is parked. The invention also relates to an image pickup device having lens optical systems of various types of cameras.

In the past, various types of image pickup devices such as an on-board type camera, a monitoring camera, etc. have been known. For instance, in the on-board type cameras disclosed in the Japanese Patent Publications JP-A-2007-163549 or JP-A-2006-11093, an effective field angle in horizontal direction is about 180°. Also, it is about 180° in the image pickup device disclosed in JP-A-2007-328030.

Also, JP-A-2007-163549 discloses a lens system with a second lens group where a plastic lens, a diaphragm, and a plastic lens are arranged with the diaphragm therebetween. In claim 6 of JP-A-2007-163549, lens design is defined on the condition: −0.5<flaf/flar<0 (where flaf and flar represent two focal distances adjacent to each other respectively with a diaphragm between them). In this type of lens design, an effective field angle cannot be attained in horizontal direction.

In JP-A-2006-11093, the conditions are set to: 0.3<|fpnx/fppx|<0.6, and 0.3<|fpny/fppy|<0.6. As a result, in JP-A-2006-11093, an effective field angle cannot be attained in horizontal direction.

Here, when it is assumed that optical axis is Z-axis and that X-axis and Y-axis perpendicularly cross the Z-axis, it is defined as follows:

fpnx: X-Z section paraxial focal distance of a negative lens made of plastic material; fppx: X-Z section paraxial focal distance of a positive lens made of plastic material; fpny: Y-Z section paraxial focal distance of a negative lens made of plastic material; and fppy: Y-Z section paraxial focal distance of a positive lens made of plastic material. As a described above, in the conventional type image pickup device, an effective field angle is about 180°, and it is not possible to attain the effective field angle to 200° or more at maximum in horizontal direction. Further, it is not possible to accomplish an anamorphic optical system with high projection characteristics and high resolving power in particular, and it is not possible to realize anamorphic magnification, which is not influenced by temperature conditions, either.

It is an object of the present invention to develop an anamorphic optical system, which has an effective field angle of 200° or more at maximum in horizontal direction and has high projection characteristics and high resolving power in particular, and also to provide this anamorphic optical system on an image pickup device such as an on-board type camera, a monitoring camera, etc., and further to provide an image pickup device, an on-board type camera, and a monitoring camera, which have an effective field of angle of 200° or more at maximum in horizontal direction.

Describing in more detail, it is an object of the present invention to provide an image pickup device comprising an optical system, which has high projection characteristics closer to stereoscopic projection, has a high resolving power in particular on outside axis, has an effective field angle of 200° or more at maximum in horizontal direction, or an effective field angle of at least about 220° at maximum and has precise anamorphic magnification. Also, it is an object of the present invention to provide an on-board type camera, which has such type of lens system as to take images inside or outside a vehicle. Also, it is an object of the present invention to provide a monitoring camera, which has such type of lens system as to take and record images inside or outside a moving object such as an automobile while the automobile is being driven or is parked.

To obtain the above objects, the present invention provides an image pickup device, which comprises one aspheric lens and one anamorphic lens on object side and one aspheric lens and one anamorphic lens on image side with a diaphragm therebetween, and is provided with an anamorphic optical system, which has an effective field angle of 200° or more at maximum in horizontal direction.

The invention also provides an on-board type camera, which comprises one aspheric lens and one anamorphic lens on object side and one aspheric lens and one anamorphic lens on image side with a diaphragm therebetween, and is provided with an anamorphic optical system, which has an effective field angle of 200° or more at maximum in horizontal direction.

Also, the invention provides a monitoring camera, which comprises one aspheric lens and one anamorphic lens on object side and one aspheric lens and one anamorphic lens on image side with a diaphragm therebetween, and is provided with an anamorphic optical system, which has an effective field angle of 200° or more at maximum in horizontal direction.

The present invention provides an anamorphic optical system, which comprises one aspheric lens and one anamorphic lens on object side and one aspheric lens and one anamorphic lens on image side with a diaphragm therebetween, and is provided with an anamorphic optical system, which has an effective field angle of 200° or more at maximum in horizontal direction. As a result, it is possible to attain an anamorphic optical system having high projection characteristics and high resolving power in particular and to realize anamorphic magnification not influenced by temperature conditions.

FIG. 1 is a horizontal cross-sectional view of an anamorphic optical system of an image pickup device according to the present invention;

FIG. 2 is a vertical cross-sectional view of an anamorphic optical system of an image pickup device according to the present invention;

FIG. 3 is a table to show lens data of the anamorphic optical system;

FIG. 4 is a table to show data of an anamorphic surface of a fifth surface;

FIG. 5 is a table to show data of an anamorphic surface of a sixth surface;

FIG. 6 is a table to show data of an anamorphic surface of a sixteenth surface;

FIG. 7 is a table to show data of an anamorphic surface of a seventeenth surface;

FIG. 8 is a table to show aspheric data of a ninth surface;

FIG. 9 is a table to show aspheric data of a tenth surface;

FIG. 10 is a table to show aspheric data of a fourteenth surface;

FIG. 11 is a table to show aspheric data of a fifteenth surface;

FIG. 12 are graphs to show aberration in horizontal direction of an anamorphic optical system of the present invention;

FIG. 13 are graphs to show aberration in vertical direction of an anamorphic optical system of the present invention;

FIG. 14 is a graph to show projection characteristics in horizontal direction of the anamorphic optical system of the present invention;

FIG. 15 is a graph to show projection characteristics in vertical direction of the anamorphic optical system of the present invention;

FIG. 16 is a table to show each anamorphic magnification (fh and fv) in horizontal direction and in vertical direction of a third lens G 3 and an eighth lens G 8 ;

FIG. 17 is a table to show focal distance ratio (fv/fh) obtained by calculation of the third lens G 3 and the eighth lens G 8 ;

FIG. 18 is a graph to show each anamorphic magnification in horizontal direction and in vertical direction of the third lens G 3 ; and

FIG. 19 is a graph to show each anamorphic magnification in horizontal direction and in vertical direction of the eighth lens G 8 .

Description will be given below on the best aspect for carrying out the invention by referring to the attached drawings.

FIG. 1 and FIG. 2 represent respectively a horizontal cross-sectional view and a vertical cross-sectional view of an anamorphic optical system 1 of an image pickup device according to the present invention.

The anamorphic optical system 1 comprises 9 lenses. From a diaphragm s 11 toward object side, there are arranged five lenses, i.e. a first lens G 1 , a second lens G 2 , a third lens G 3 , a fourth lens G 4 , and a fifth lens G 5 . From the diaphragm s 11 toward image side, four lenses are arranged: a sixth lens G 6 , a seventh lens G 7 , an eighth lens G 8 , and a ninth lens G 9 .

Lens surfaces of these 9 lenses are referred from object side as s 1 to s 10 and s 12 to s 19 respectively. Some of symbols of the lens surfaces are not shown in the figure.

The first lens G 1 is a lens made of glass. The third lens G 3 , the fifth lens G 5 , the seventh lens G 7 and the eighth lens G 8 are made of resin such as plastics. The other lenses are glass lenses. The ninth lens 9 is simply a glass plate.

The first lens G 1 has a large aperture. In the fifth lens G 5 , each of a first surface s 9 and a second surface s 10 is an aspheric surface. Also, in the seventh lens G 7 , each of a first surface s 14 and a second surface s 15 is designed as an aspheric surface. Each of the third lens G 3 and the eighth lens G 8 is designed as an anamorphic lens.

FIG. 3 is a table to show lens data of an anamorphic optical system of an image pickup device according to the present invention. That is, the table shows lens data with respect to each of the lens surfaces s 1 to s 10 , the diaphragm s 11 and the lens surfaces s 12 to s 19 of the anamorphic optical system. And lens data are radius of curvature in each of horizontal direction and vertical direction, distance between surfaces, refractive index (nd) and Abbe number (νd).

FIG. 4 shows anamorphic surface data of the fifth surface s 5 , FIG. 5 shows anamorphic surface data of the sixth surface s 6 , FIG. 6 shows anamorphic surface data of the sixteenth surface s 17 , and FIG. 7 shows anamorphic surface data of the seventeenth surface s 18 , respectively.

FIG. 8 shows aspheric data of the ninth surface s 9 , FIG. 9 shows aspheric data of the tenth surface s 10 , FIG. 10 shows aspheric data of the fourteenth surface s 15 , and FIG. 11 shows aspheric data of the fifteenth surface s 16 , respectively.

FIG. 12 and FIG. 13 show graphs of aberration in horizontal direction and vertical direction of the anamorphic optical system 1 of the present invention respectively. Condition of spherical aberration, astigmatic, and distortion aberration with respect to three primary colors, i.e. red color (wavelength 656 nm), green color or yellow color (wavelength 587 nm), and blue color (wavelength 486 nm) are shown respectively.

FIG. 14 shows projection characteristics in horizontal direction of the anamorphic optical system 1 of the present invention. FIG. 15 shows projection characteristics in vertical direction.

An equi-distant projection is shown in approximately linear (straight-line) graph both in horizontal and vertical directions, and a stereoscopic projection is also represented in approximately linear (straight-line) graph. However, in the stereoscopic projection in horizontal direction, when it goes beyond a semi-field angle 90°, an image height increases drastically and when it goes beyond a semi-field angle 110°, the image height goes beyond 2.5 mm easily and reaches nearly as high as 3.0 mm.

The third lens G 3 and the eighth lens G 8 are anamorphic lenses, and anamorphic magnification of each lens is as shown in FIG. 16 .

In the third lens G 3 , with the increase of anamorphic magnification in vertical direction, the focal distance increases in a direction of negative (−) number. In particular, in case where the magnification is 1.6 or more, magnification of the third lens G 3 drastically increases in the direction of negative (−) number. In the eighth lens G 8 , with the increase of magnification in vertical direction, the focal distance increases in the direction of positive (+) number. In particular, in case where magnification is 1.6 or more, magnification of the eighth lens G 8 drastically increases in the direction of positive (+) number.

It is assumed here that practical anamorphic magnification is 1.0 to 2.0 times. Between these magnification values, a focal distance in horizontal direction (fh) and a focal distance in vertical direction (fv) in each of the third lens G 3 and the eighth lens G 8 were calculated. Further, based on the results of this calculation, a focal distance ratio (fv/fh) was calculated.

FIG. 17 shows the focal distance ratio (fv/fh) obtained by the calculation. FIG. 18 shows the values of anamorphic magnification in each of horizontal direction and vertical direction of the third lens G 3 , and FIG. 19 shows the values of anamorphic magnification in each of horizontal direction and vertical direction of the eighth lens G 8 .

As described above, in the Japanese Patent Publication JP-A-2006-11093, the condition is: 0.3<|fpnx/fppx|<0.6, and 0.3<|fpny/fppy|<0.6. However, according to the present invention the condition is: |fpnx/fppx|=1.21, |fpny/fppy|=1.26. While maintaining the effective focal distance, temperature characteristics are balanced well as a whole. Also, the lens is so designed that the effective field angle can be obtained in horizontal direction. According to the present invention, the above relationship can be satisfied by the focal distances in horizontal direction and in vertical direction of G 3 and G 8 respectively.

As described above, curvatures are changed in each of horizontal direction and vertical direction. The focal distance ratio is adjusted, and an aspheric surface is attained to have high resolution in each direction and aspheric surface is accomplished in order to emphasize images in the surrounding. Also, projection characteristics are brought closer to the stereoscopic projection and in particular, the resolving power outside the axis is increased. As a result, it is possible to increase effective field angle to 200° or more at maximum in horizontal direction and to at least 220° at maximum and it is possible to accomplish an precise anamorphic magnification. Further, it is possible to realize an anamorphic optical system with high projection characteristics and high resolving power in particular and to accomplish an anamorphic magnification, which is not influenced by temperature conditions.

When the anamorphic optical system 1 of the present invention is applied to an image pickup device, to an on-board type camera for taking images inside or outside the vehicle, or to a monitoring camera for taking and recording images inside or outside the vehicle while a moving object such as an automobile is being driven or is parked, it is possible to provide an image pickup device and an on-board camera, which can attain an effective field angle of 200° at maximum, and at least about 220° at maximum, and can accomplish a precise anamorphic magnification and can have temperature characteristics to endure environmental changes.