WO2021196057A1

WO2021196057A1 - Optical lens, imaging device, electrical device, method of manufacturing the same

Info

Publication number: WO2021196057A1
Application number: PCT/CN2020/082650
Authority: WO
Inventors: Tetsuji Kamata
Original assignee: Guangdong Oppo Mobile Telecommunications Corp., Ltd.
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2021-10-07

Abstract

An optical lens (40) includes at least one lens element and a casing to accommodate the lens. The optical lens (40) satisfies a condition that an MTF _A is equal to or greater than D ₁₀₀Co X MTF ₀. The MTF _A is an X-coordinate of the MTF curve in a second coordinate system when the percentage of an image height H is H _A, the H _A is a Y-coordinate of an intersection point of a first linear line and a second linear line of a distortion curve in a first coordinate system, the distortion ratio D ₁₀₀ is a distortion ratio D at 100 percent of the image height H ₁₀₀, the MTF ₀ is a percentage of the contrast MTF when the percentage of the image height H ₀ is 0, and the C ₀ is a coefficient to adjust a minimum percentage of the contrast MTF _A.

Description

OPTICAL LENS, IMAGING DEVICE, ELECTRICAL DEVICE, METHOD OF MANUFACTURING THE SAME

FIELD

The present disclosure relates to an optical lens, an imaging device, an electrical device, and a method of manufacturing the same.

BACKGROUND

Nowadays, a lot of electrical devices have an imaging device to take pictures anytime and anywhere. One of the most popular electrical devices equipped with such imaging device is a smartphone.

In order to reduce a thickness of the electrical device, either the imaging device with small imaging sensor is employed in the electrical device, or a thicker projection part for the imaging device is partially formed in the electrical device. The projection part of the electrical device be sometimes damaged and restricts a freedom of the design of the electrical device.

In the past few decades, a technology of downsizing is one of the typical challenges in optical design. This resulted in a lot of technologies of modifying the optical lens itself so as to achieve downsizing. However, such techniques are becoming insufficient, because users demand thinner electrical devices for their portability and their more pleasing appearance.

SUMMARY

The present disclosure aims to solve at least one of the technical problems mentioned above. Accordingly, the present disclosure needs to provide an optical lens, an imaging device, an electrical device, and a method of manufacturing the same.

In accordance with the present disclosure, an optical lens may include at least one lens element and a casing to accommodate the lens element, wherein an object to be imaged is located at a first side of the optical lens and an imaging sensor to capture an object image of the object is located at a second side of the optical lens, the second side of the optical lens being an opposite side of the first side of the optical lens, wherein

a distortion curve of the optical lens represented in a first coordinate system is linearized by at least a first linear line and a second linear line, wherein an X-axis of the first coordinate system is a distortion ratio D and a Y-axis of the first coordinate system is a percentage of an image height H of the object image on the imaging sensor,

the first linear line approximates a lower part of the image height of the distortion curve in the first coordinate system and the second linear line approximates a higher part of the image height of the distortion curve in the first coordinate system,

an angle α ₁ is greater than an angle α ₂, where the angle α ₁ is an angle formed by the first linear line and the X-axis of the first coordinate system, and the angle α ₂ is an angle formed by the second linear line and the X-axis of the first coordinate system,

an MTF (Modulation Transfer Function) curve of the optical lens is represented in a second coordinate system, wherein an X-axis of the second coordinate system is a percentage of a contrast MTF, and a Y-axis of the second coordinate system is the percentage of the image height H of the object image on the imaging sensor, and

the optical lens satisfies a condition that an MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X Co X MTF ₀, where

the MTF _A is an X-coordinate of the MTF curve in the second coordinate system when the percentage of the image height H is H _A,

the H _A is a Y-coordinate of an intersection point of the first linear line and the second linear line of the distortion curve in the first coordinate system,

the distortion ratio D ₁₀₀ is the distortion ratio D at 100 percent of the image height H ₁₀₀,

the MTF ₀ is the percentage of the contrast MTF when the percentage of the image height H ₀ is 0, and

the Co is a coefficient to adjust a minimum percentage of the contrast MTF _A.

In some embodiments, the coefficient Co may be 10.

In some embodiments, the MTF curve in the second coordinate system may be described based on a 1/4 Nyquist frequency.

In some embodiments, the MTF curve in the second coordinate system may be described based on a tangential orientation.

In some embodiments, the optical lens may further satisfy a condition that an MTF ₁₀₀ is equal to or greater than the distortion ratio D ₁₀₀ X Co ₁₀₀ X MTF ₀, where

the MTF ₁₀₀ is the percentage of the contrast MTF when the percentage of the image height H ₁₀₀ is 100, and

the Co ₁₀₀ is a coefficient to adjust a minimum percentage of the contrast MTF ₁₀₀ at 100 percent of the image height H ₁₀₀.

In some embodiments of this case, the coefficient Co may be 9 and the coefficient Co ₁₀₀ may be 7.

In accordance with the present disclosure, an imaging device may include:

the optical lens mentioned above; and

the imaging sensor, on which the optical lens forms the object image.

In some embodiments, a position of 100 percent of an image height H ₁₀₀ of the object image may be located at a corner of the imaging sensor.

In some embodiments, the object image on the imaging sensor may be subjected to a distortion correction process to generate a final target image.

In some embodiments, the optical lens may generate a pincushion distortion,

an edge of the final target image may be decided based on the corner of the object image at the corner of the imaging sensor, and

an outside region of the object image which is outside the final target image may be cut out when the final target image is generated.

In some embodiments, a distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ of the object image of the optical lens may be equal to or greater than 5 percent and equal to or less than 10 percent.

In some embodiments, the percentage of the image height H _A may be equal to or greater than 20 percent and equal to or less than 50 percent.

In accordance with the present disclosure, an electrical device may include:

the imaging device mentioned above; and

a distortion correction processor configured to execute the distortion correction process to correct a distortion of the object image on the imaging sensor to generate the final target image.

In accordance with the present disclosure, a method of manufacturing an optical lens may include:

providing a casing;

providing at least one lens element;

assembling the casing and the lens element into the optical lens so that an object to be imaged is located at a first side of the optical lens and an imaging sensor to capture an object image of the object is located at a second side of the optical lens, the second side of the optical lens being an opposite side of the first side of the optical lens, wherein

the Co is a coefficient to adjust a minimum percentage of the contrast MTF _A.

In some embodiments, the coefficient Co may be 10.

In some embodiments of this case, coefficient Co may be 9 and the coefficient Co ₁₀₀ may be 7.

In accordance with the present disclosure, a method of manufacturing an imaging device may include:

providing a support member;

providing the optical lens mentioned above;

providing the imaging sensor; and

assembling the support member, the optical lens and the imaging sensor into the imaging device.

In some embodiments, the optical lens may generate a pincushion distortion,

In accordance with the present disclosure, a method of manufacturing an electrical device may include:

providing the imaging device mentioned above;

providing a distortion correction processor configured to execute the distortion correction process to correct a distortion of the object image on the imaging sensor to generate the final target image; and

assembling the imaging device and the distortion correction processor into the electrical device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of embodiments of the present disclosure will become apparent and more readily appreciated from the following descriptions made with reference to the drawings, in which:

FIG. 1 is a schematic plan view of an electrical device equipped with an imaging device according to one of embodiments of the present disclosure;

FIG. 2 is a cross sectional view taken along line II-II of the electrical device equipped with the imaging device of FIG. 1;

FIG. 3 illustrates a focal length f of the imaging device in no aberration case (Ideal Optical Lens Case) ;

FIG. 4 illustrates the imaging sensor and a percentage of an image height on an imaging sensor;

FIG. 5 illustrates a distortion curve of the optical lens in no aberration case (Ideal Optical Lens Case) ;

FIG. 6 illustrates the focal length f' of the imaging device in a positive distortion aberration case (Actual Optical Lens Case) ;

FIG. 7 illustrates the imaging sensor and the percentage of the image height on the imaging sensor;

FIG. 8 illustrates the distortion curve of the optical lens in the positive distortion aberration case (Actual Optical Lens Case) ;

FIG. 9 illustrates a degradation of a sharpness of an object image (final target image) after a distortion correction process;

FIG. 10 illustrates the focal length f and the focal length f' of the imaging device according to the present embodiment;

FIG. 11 illustrates the imaging sensor and the object images overlapped with the imaging sensor;

FIG. 12 illustrates a distortion correction processor, the object image before the distortion correction process and the object image (final target image) after the distortion correction process;

FIG. 13 illustrates an example of an MTF (Modulation Transfer Function) curve of the optical lens of the imaging device;

FIG. 14 illustrates a first graph of the distortion curve and a second graph of the MTF curve of the optical lens of the imaging device of the present embodiment in order to show a relationship between the distortion curve and the MTF curve;

FIG. 15 shows conditions which the distortion curve and the MTF curve represented in FIG. 14 should satisfy;

FIG. 16 illustrates the first graph of the distortion curve and the second graph of the MTF curve of the optical lens of the imaging device of the present embodiment in a case where two minimum percentages of the contrast MTF are defined;

FIG. 17 shows conditions which the distortion curve and the MTF curve represented in FIG. 16 should satisfy;

FIG. 18 illustrates the first graph of the distortion curve and the second graph of the MTF curve of the optical lens of the imaging device of the present embodiment in a case where the distortion curve is linearized by three lines; and

FIG. 19 illustrates an internal structure of the optical lens according to the present embodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detail and examples of the embodiments will be illustrated in the accompanying drawings. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions. The embodiments described herein with reference to the drawings are explanatory, which aim to illustrate the present disclosure, but shall not be construed to limit the present disclosure.

FIG. 1 illustrates an electrical device 10 according to one of embodiments of the present disclosure and FIG. 2 illustrates a cross sectional view taken along line II-II of the electrical device of FIG. 1. In other words, FIG. 1 illustrates a layout of a first side of the electrical device 10.

As shown in FIGS. 1 and 2, the electrical device 10 may include an imaging device 20 and a distortion correction processor 22. In other words, the imaging device 20 and the distortion correction processor 22 are assembled into the electrical device 10. The imaging device 20 captures an object image of an object to be imaged. The imaging device 20 may include a protective glass 30, an optical lens 40 and an imaging sensor 50. In the present embodiment, the optical lens 40 may be composed of one lens element or a combination of a plurality of lens elements.

Here, a first side of the imaging device 20 and the optical lens 40 indicates a side in which an object to be imaged by the imaging device 20 is located, and a second side of the imaging device 20 and the optical lens 40 indicates a side in which the imaging sensor 50 is located. The second side of the imaging device 20 and the optical lens 40 is an opposite side of the first side. As a result, when a user of the electrical device 10 captures the object image of the object by using the electrical device 10, the object is located at the first side of the imaging device 20 and the optical lens 40.

The electrical device 10 may be, for example, a smartphone, a tablet computer, a notebook type computer, and others. When the electrical device 10 is designed, a thickness of the electrical device 10 is mainly determined by a height H _imd of the imaging device 20 and the height H _imd of the imaging device 20 is mainly determined by a focal length f of the imaging device 20. Therefore, the thickness of the electrical device 10 is substantially determined by the focal length f of the imaging device 20. In other words, the shorter focal length f can reduce the height H _imd of the imaging device 20 and the shorter height H _imd of the imaging device 20 can reduce the thickness of the electrical device 10.

The distortion correction processor 22 executes a distortion correction process to correct a distortion of the object image to generate a final target image which is the object image the user would like to capture. Although the electrical device 10 according to the present embodiment has the distortion correction processor 22, the distortion correction processor 22 may be omitted in the electrical device 10. In this case, the distortion correction process is executed in other electrical device, for example, in a personal computer, a notebook computer and so on.

FIG. 3 illustrates the focal length f of the imaging device 20 in no aberration case (Ideal Optical Lens Case) , FIG 4 illustrates the imaging sensor 50 and a percentage of an image height H on the imaging sensor 50, and FIG. 5 illustrates a distortion curve of the optical lens 40 shown in FIG. 3.

As shown in FIG. 3, the focal length f is a distance between a center of the optical lens 40 and the imaging sensor 50. An angle θ indicates an angle between a center light input to the center of the optical lens 40 and a light input to the optical lens 40. An angle θ indicates an angle between a center light passing through the center of the optical lens 40 and a light input to the optical lens 40, whereas an angle θ' indicates an angle between the center light passing though the center of the optical lens 40 and a light output from the optical lens 40. In the ideal optical lens, the angle θ of the light input to the optical lens 40 is equal to the angle θ' of the light output from the optical lens 40.

As shown in FIG. 4, the imaging sensor 50 may include M X N pixels, 0 percent of the image height H ₀ corresponds to a center of the

imaging sensor

50, and 100 percent of the image height H ₁₀₀ corresponds to a corner C _IMG of the imaging sensor 50. In this case, 100 percent of the image height H ₁₀₀ is a length H _r between the center of the imaging sensor 50 and the corner C _IMG of the imaging sensor 50. In the ideal optical lens 40, the object image of the object on the imaging sensor 50 is not distorted.

Therefore, as shown in FIG. 3, 100 percent of the image height H ₁₀₀ and the length H _r is expressed by f X tan θ, or they may also be expressed by f X tan θ' because tan θ is equal to tan θ' in the ideal optical lens 40.

As shown in FIG. 5, the distortion curve of the ideal optical lens 40 is represented on a coordinate system in which an X-axis is a distortion ratio D and a Y-axis is a percentage of the image height H of the object image on the imaging sensor 50. In the distortion curve of the optical lens 40 of the ideal optical lens 40, the distortion ratio D is always 0 percent. That is, the distortion ratio D ₀ at 0 percent of the image height H ₀ is 0 percent and the distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ is also 0 percent.

FIG. 6 illustrates the focal length f of the imaging device 20 in a positive distortion aberration case (Actual Optical Lens Case) , FIG 7 illustrates the imaging sensor 50 and the percentage of the image height H on a plane of the imaging sensor 50, and FIG. 8 illustrates the distortion curve of the optical lens 40 shown in FIG. 6. FIG. 6, FIG. 7 and FIG. 8 correspond to FIG. 3, FIG. 4 and FIG. 5 mentioned above, respectively.

As shown in FIG. 6, the focal length f is a distance between the center of the optical lens 40 and the imaging sensor 50. The angle θ also indicates an angle between the center light input to the center of the optical lens 40 and the light input to the optical lens 40. The angle θ' also indicates the angle between the center light passing though the center of the optical lens 40 and the light output from the optical lens 40. In the actual optical lens 40, the angle θ of the light input to the optical lens 40 is not equal to the angle θ' of the light output from the optical lens 40 because of an aberration of the optical lens 40. The example of the optical lens 40 shown in FIG. 6 generates a positive distortion aberration.

As shown in FIG. 7, the imaging sensor 50 may also include M X N pixels, and 0 percent of the image height H ₀ corresponds to the center of the imaging sensor 50, but 100 percent of the image height H ₁₀₀ corresponds to an outside of the imaging sensor 50. That is, 100 percent of the image height H ₁₀₀ does not correspond to the corner C _IMG of the imaging sensor 50 because of the distortion of the object image.

As a result, a length from 0 percent of the image height H ₀ to 100 percent of the image height H ₁₀₀ does not correspond to the length H _r between the center of the imaging sensor 50 and the corner C _IMG of the imaging sensor 50.

Therefore, as shown in FIG. 6, 100 percent of the image height H ₁₀₀ of the object image on the plane of the imaging sensor 50 is not expressed by f X tan θ but it is express by f X tan θ', where an angle θ' is an angle between the center light and a light forming the corner of the object image of the object on the plane of the imaging sensor 50.

As shown in FIG. 8, in the distortion curve of the optical lens 40 of the actual optical lens, the distortion ratio D is gradually increased as the image height H is increased. That is, a graph of a relationship between the distortion ratio D and the image height H is curved as the image height H is increased. In an example of the distortion curve shown in FIG. 8, the distortion ratio D ₀ at 0 percent of the image height H ₀ is 0 percent but the distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ is a certain percentage.

The distortion of the object image has to be corrected by means of the distortion correction process to obtain the natural object image (final target image) . However, a sharpness of the object image which has been corrected by the distortion correction process is degraded as shown in FIG. 9.

In FIG. 9, a center part around the center of the corrected object image (final target image) is a sharpness degradation area due to the distortion correction process. This is because, in a unit area in the final target image, an image information quantity in the center part of the object image is less than an image information quantity in a peripheral part of the object image which is outside the center part of the object image.

As mentioned above, in order to lower the height H _imd of the imaging device 20, the focal length f should be shortened. Therefore, in the electrical device 10 of the present embodiment, the focal length f of the imaging device 20 is shortened to the focal length f'.

FIG. 10 illustrates the focal length f' of the imaging device 20 according to the present embodiment, and FIG. 11 illustrates the object image 52 and the object image 54 which are overlapped with the imaging sensor 50.

As shown in FIG. 10, the focal length f' is shorter than the focal length f and thus the height H _imd of the imaging device 20 can be reduced and the imaging device 20 can be smaller. In other words, the optical lens 40 of the imaging device 20 according to the present embodiment is closer to the imaging sensor 50.

As shown in FIG. 11, the optical lens 40 with the focal length f illustrated in FIG. 6 generates the object image 52 whereas the optical lens 40 with the focal length f' illustrated in FIG. 10 generates the object image 54. The object image 52 is subjected to the distortion correction process to correct the distortion of the object image 52. Also, the object image 54 is subjected to the distortion correction process to correct the distortion of the object image 54.

The object image 52 subjected to the distortion correction process is wider than the object image 54 subjected to the distortion correction process. In other words, the object image 52 is wider than the imaging sensor 50, whereas the object image 54 is within a size of the imaging sensor 50.

More specifically, there are four corners 54a in the object image 54 and there are four corners 50a in the imaging sensor 50. Each of the corners 54a of the object image 54 is located at each of the corners 50a of the imaging sensor 50. That is, four of the corners 54a of the object image 54 are located at four of the corners 50a of the imaging sensor 50, respectively.

Therefore, a positon of 100 percent of the image height H ₁₀₀ of the object image 54 on the imaging sensor 50 is located at the corner 50a of the imaging sensor 50.

There are four edges 54b between the corners 54a in the object image 54 on the imaging sensor 50. The four edges 54b of the object image 54 are decided based on the corners 54a of the object image 54 at the corners 50a of the imaging sensor 50. In the present embodiment, the optical lens 40 generates a pincushion distortion. Therefore, each of the four edges 54b is curved inwardly, and the four edges 54b are also within the size of the imaging sensor 50.

In the present embodiment, the light passing through the optical lens 40 may reach an outside region of the object image 54. Therefore, both an inside region inside the object image 54 and an outside region outside the object image 54 are subjected to the distortion correction process, and the outside region is cut out to create the final target image without distortion by the inside region of the object image 54.

Alternatively, the distortion correction process may be applied only to the inside region of the object image 54. That is, the inside region inside the object image 54 is defined by the four edges 54b, and the distortion correction process is executed for the inside region of the object image 54 to correct the distortion of the object image 54. Alternatively, the outside region of the object image 54 may be cut out before the distortion correction process.

As shown in FIG. 10 and FIG. 11, 100 percent of the image height H ₁₀₀ of the object image 54 is expressed by f' X tan θ" , where the angle θ" is an angle between the center light and a light forming the corner 54a of the object image 54 of the object on the plane of the imaging sensor 50. An angle between the center light and a light forming the edges 54b other than the corners 54a is less than the angle θ" . In other words, the angle θ" is the greatest angle between the center light and the light forming the corners 54a and the edges 54b of the object image 54 on the plane of the imaging sensor 50.

FIG. 12 illustrates the distortion correction processor 22, the object image 54 before the distortion correction process and the object image 54 after the distortion correction process which is the final target image the user would like to obtain.

As shown in FIG. 12, the distortion correction processor 22 executes the distortion correction process for the object image 54. Before the distortion correction process, the object image 54 is distorted and thus the edges 54b of the object image 54 are curved inwardly.

Therefore, the distortion correction processor 22 stretches the object image 54 to correct the distortion of the object image 54 and generate the final target image. More specifically, the distortion correction processor 22 stretches the object image 54 outwardly in the distortion correction process. That is, the object image 54 is outwardly extended on all sides.

The distortion correction processor 22 stretches the object image 54 in accordance with, for example, a bicubic interpolation, a bilinear interpolation, or the like. However, the distortion correction processor 22 may stretch the object image 54 in accordance with other methods.

After the distortion correction process has been applied to the object image 54, the distortion of the object image 54 is substantially eliminated and thus the edges 54b of the object image 54 become substantially straight.

However, as explained with reference to FIG. 9, the center part of the object image 54 is degraded due to the distortion correction process. For the user of the electrical device 10, the center part of the object image 54 is the most important because a region of interest is often located around the center of the object image 54. Here, the sharpness degradation of the object image 54 is relevant to the distortion curve of the optical lens 40.

Moreover, the sharpness degradation of the object image 54 is also relevant to an optical resolution performance, for example, an MTF (Modulation Transfer Function) . FIG. 13 shows an MTF curve of the optical lens 40 as an example. In FIG. 13, an X-axis is the percentage of the image height H, and a Y-axis is a percentage of contrast MTF. The percentage of the contrast MTF at 0 percent of the image height H ₀ is a certain percent which depends on characteristics of the optical lens 40, and the percentage of the contrast MTF is gradually decreased in accordance with increasing the image height H.

If the percentage of the contrast MTF is high, it means that the optical lens 40 can create a fine image on the imaging sensor 50. In other words, if the percentage of the contrast MTF is high, a high spatial frequency can be reproduced on the imaging sensor 50. As shown in FIG. 13, characteristics of the spatial frequency in the center part of the object image 54 are relatively high, whereas characteristics of the spatial frequency in the peripheral part of the object image 54 are relatively low.

Therefore, according to the optical lens 40 of the present embodiment, in order to improve and suppress the degradation of the object image, a combination of the distortion curve and the MTF curve is adjusted so that the center part of the object image 54 is clearer and sharper.

FIG. 14 illustrates a first graph of the distortion curve DC and a second graph of the MTF curve MC of the optical lens 40 of the imaging device 20 of the present embodiment in order to show a relationship therebetween.

As shown in FIG. 14, the distortion curve DC of the first graph of the optical lens 40 is represented in a first coordinate system, an X-axis of the first coordinate system is the distortion ratio D of the object image 54, and a Y-axis of the first coordinate system is a percentage of the image height H of the object image on the plane of the imaging sensor 50.

On the other hand, the MTF curve of the second graph of the optical lens 40 is represented in a second coordinate system, an X-axis of the second coordinate system is a percentage of the contrast MTF, and a Y-axis of the second coordinate system is a percentage of the image height H of the object image on the plane of the imaging sensor 50.

The MTF curve MC according to the present embodiment is described based on a 1/4 Nyquist frequency. Moreover, the MTF curve MC according to the present embodiment is described based on a tangential orientation. That is, according to the present embodiment, the MTF curve MC is based on test grids oriented in tangential direction to an optical axis of the optical lens 40. As well known, a 1/2 Nyquist frequency is the maximum frequency of the image which can be reproduced by the optical lens 40. Therefore, the 1/4 Nyquist frequency is a half of the maximum frequency of the image which can be reproduced by the optical lens 40. The 1/4 Nyquist frequency is a reasonable and appropriate frequency to evaluate the characteristics of the optical lens 40, because it is not too fine and not too rough for the test grids.

However, the 1/4 Nyquist frequency is one of the examples of the frequency for the MTF curve MC to evaluate the characteristics of the optical lens 40, and the other frequency of the test grids may be used to describe the MTF curve MC. In addition, test grids oriented in a radial direction to the optical axis of the optical lens 40 may be used to describe the MTF curve MC instead of the test grids oriented in the tangential direction.

In the first graph of the distortion curve DC, a minimum of the percentage of the image height H ₀ is 0 and it is located at the origin of the first coordinate system. A maximum of the percentage of the image height H ₁₀₀ is 100 and it is located on the Y-axis of the first coordinate system. 0 percent of the image height H ₀ corresponds to the center of the

object image

54, and 100 percent of the image height H ₁₀₀ corresponds to the corners 54a of the object image 54 on the plane of the imaging sensor 50.

Also, in the first graph of the distortion curve DC, a minimum of the distortion ratio D ₀ is 0 and it is located at the origin of the first coordinate system. A maximum of the distortion ratio D ₁₀₀ depends on the characteristics of the optical lens 40. The distortion ratio D ₀ indicates the distortion ratio at the center of the object image 54, and the distortion ratio D ₁₀₀ indicates the distortion ratio at the corners 54a of the object image 54.

In the present embodiment, the distortion ratio D is expressed by (AD-PD) /PD X 100%. The predicted distance PD indicates a distance from the center of the object image to an ideal point where the object should be imaged. The actual distance AD indicates a distance from the center of the object image to an actual point where the object is actually imaged.

On the other hand, in the second graph of the MTF curve MC, a minimum of the percentage of the image height H ₀ is also 0 and it is also located at the origin of the second coordinate system. A maximum of the percentage of the image height H ₁₀₀ is also 100 and it is also located on the Y-axis of the second coordinate system. That is, the Y-axis of the second coordinate system of the second graph of the MTF curve MC is the same as that of the first coordinate system of the first graph of the distortion curve DC.

Also, in the second graph of the MTF curve MC, the percentage of the contrast MTF depends on the characteristics of the optical lens 40 from 0 percent of the image height H ₀ to 100 percent of the image height H ₁₀₀. When the percentage of the image height H ₀ is 0, the percentage of the contrast MTF is indicated by MTF ₀, whereas, when the percentage of the image height H ₁₀₀ is 100, the percentage of the contrast MTF is indicated by MTF ₁₀₀. As understood from the second graph of the MTF curve MC, the percentage of the contrast MTF in the center part of the optical lens 40 is high, but the percentage of the contrast MTF in the peripheral part, which is outside the center part, is low. In other words, the percentage of the contrast MTF is gradually decreased in accordance with the increase of the percentage of the image height H.

Incidentally, the distortion curve DC and the MTF curve MC illustrated in FIG. 14 shows the characteristics of the design of the optical lens 40 or the characteristics of the actual optical lens 40. That is, the characteristics of mass-produced optical lens 40 are not the same each other, and each of them has own characteristics. Therefore, 1) the distortion curve DC and the MTF curve MC in FIG. 14 may be considered as the characteristics of the design of the optical lens 40, 2) the distortion curve DC and the MTF curve MC in FIG. 14 may be considered as the characteristics of each mass-produced optical lens 40, or 3) the distortion curve DC and the MTF curve MC in FIG. 14 may be considered as an average of the characteristics of the mass-produced optical lenses 40. Therefore, the following explanation can be applied to any kind of the distortion curve DC and the MTF curve MC.

FIG. 15 shows conditions which the distortion curve DC and the MTF curve MC represented in FIG. 14 should satisfy. Although FIG. 15 shows five conditions, i.e. a condition 1 through a condition 5, the optical lens 40 does not necessarily have to satisfy all of the five conditions 1-5. That is, the optical lens 40 may satisfy one, two, three or four conditions among the five conditions 1-5.

The distortion curve DC and the MTF curve MC of the optical lens 40 of the imaging device 20 according to the present embodiment satisfies any combinations of the following conditions 1-5.

In the first graph of the distortion curve DC, the distortion curve DC can be linearized and approximated by two or more linear lines in the first coordinate system. In the example shown in FIG. 14, the distortion curve DC can be linearized and approximated by two linear lines. That is, the distortion curve DC can be linearized and approximated by a first linear line L1 and a second linear line L2. The first linear line L1 approximates a lower part of the image height H of the distortion curve DC, and the second linear line L2 approximates a higher part of the image height H of the distortion curve DC.

For example, the first linear line L1 and the second linear line L2 can be calculated and decided by the method of least squares, i.e., the linear approximation. Of course, other method to calculate and decide the first linear line L1 and the second linear line L2 may be employed.

In the first graph of the distortion curve DC, an angle α ₁ is greater than an angle α ₂, where the angle α ₁ is an angle formed by the first linear line L1 and the X-axis of the first coordinate system and the angle α ₂ is an angle formed by the second linear line L2 and the X-axis of the first coordinate system.

If the distortion curve DC satisfies the condition 2, the sharpness of the center part of the object image can be improved, because the distortion ratio D of the first linear line L1 is less than the distortion ratio of the second linear line L2. In other words, the distortion curve DC in the lower part of the image height H is steeper than the distortion curve DC in the higher part of the image height H. The steeper distortion curve DC in the lower part of the image height H improves the sharpness of the center part of the object image and the final target image, and the degradation of the sharpness of the object image and the final target image can be suppressed.

In the first graph of the distortion curve DC, the distortion ratio D _A is less than D ₁₀₀ X (H _A/H ₁₀₀) . Here, a distortion ratio D _A is an X-coordinate of the intersection point of the first linear line L1 and the second linear line L2, and a percentage of the image height H _A is a Y-coordinate of the intersection point of the first linear line L1 and the second linear line L2 in the first coordinate system. Moreover, a percentage H ₁₀₀ is 100 percent, and a distortion ratio D ₁₀₀ is the distortion ratio at 100 percent of the image height H ₁₀₀.

If the distortion curve DC satisfies the condition 3, the sharpness of the center part of the object image and the final target image can be improved, because the distortion ratio D _A at the intersection point of the first linear line L1 and the second linear line L2 is small enough.

In the present embodiment, the percentage of the image height H _A is equal to or greater than 20 percent and equal to or less than 50 percent. In other words, the percentage of the image height H _A defines a boundary of the center part of the object image and therefore it is important for the user's satisfaction of the object image to set the percentage of the image height H _A at a reasonable value.

In the present embodiment, if the percentage of the image height H _A is less than 20 percent, a fine and clear region of the object image is too small for the user. On the other hand, if the percentage of the image height H _A is greater than 50 percent, it is too difficult for designers and engineers to design the optical lens 40 with the short focal length f'.

In the first graph of the distortion curve DC, the distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ of the object image of the optical lens 40 is equal to or greater than 5 percent and equal to or less than 10 percent.

If the optical lens 40 is positioned closer to the imaging sensor 50, the distortion ratio D of the object image on the imaging sensor 50 is increased. Conversely, if a greater value of the distortion ratio D is acceptable for the design of the optical lens 40, the optical lens 40 can be positioned closer to the imaging sensor 50 and it results in the reduction of the height H _imd of the imaging device 20.

Therefore, if the distortion ratio D is equal to or greater than 5 percent is acceptable, the height H _imd of the imaging device 20 can be reduced as compared to conventional imaging devices.

However, if the distortion ratio D is too great, it is impossible to correct the distortion of the object image on the imaging sensor 50 by the distortion correction process in the distortion correction processor 22. Therefore, in the condition 5 of the present embodiment, the maximum distortion ratio D is limited to 10 percent.

In the second graph of the percentage of the contrast MTF, an MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X 10 X MTF ₀. Here, the MTF _A is the X-coordinate of the MTF curve MC in the second graph when the percentage of the image height H is H _A. As defined in the condition 3, the H _A is a Y-coordinate of the intersection point of the first linear line L1 and the second linear line L2 of the distortion curve DC in the first graph, and the distortion ratio D ₁₀₀ is the distortion ratio D at 100 percent of the image height H ₁₀₀. The MTF ₀ is the percentage of the contrast MTF when the percentage of the image height H ₀ is 0.10 is a coefficient Co to adjust a minimum percentage of the contrast MTF _A. That is, 10 is just an example of the coefficient Co to adjust the minimum percentage of the contrast MTF _A.

For example, if the distortion ratio D ₁₀₀ is 8 percent (0.08) , then the condition 5 is calculated by 0.08 X 10 X MTF ₀ = 0.8 X MTF ₀ ≤ MTF _A. That is, the condition 5 defines that 80 percent of the MTF ₀ is the lowest value for the MTF _A. It is noted that, since the coefficient Co is 10 in the condition 5, the maximum distortion ration D ₁₀₀ has to be more than 10 percent in the condition 4. Otherwise, since the maximum distortion ration D ₁₀₀ is 10 percent in the condition 4, the coefficient Co has to be less than 10 in the condition 5.

If the MTF curve MC satisfies the condition 5, the contrast of the center part of the object image can be relatively sharpened. In addition, the percentage of the contrast MTF should match the distortion ratio D. That is, if the percentage of the contrast MTF is high or the object image is fine and sharp, then distortion ratio D should be low in order to improve the user's impression of the object image.

If the MTF curve MC satisfies the condition 5, the center part of the object image can be fine and sharp, and the distortion ratio D of the center part of the object image should be relatively low as well. As a result, the sharpness of the center part of the object image can be improved. As previously mentioned, the sharpness of the center part of the object image is most important for the user of the electrical device 10. Therefore, the user's satisfaction with the object image captured by the imaging device 20 can increase.

Moreover, in the MTF curve MC, the percentage of the contrast MTF is approximately decreased in accordance with the percentage of the image height H is increased. Therefore, it is expected that the percentage of the contrast MTF in an area, where the percentage of the image height H is less than the percentage of the image height H _A, would be higher than the MTF _A. As a result, although only the minimum percentage of the contrast MTF only at the percentage of the image height H _A is defined, the improvement of the sharpness in the center part of the object image can be achieved.

In the example of the MTF curve MC shown in FIG. 14, only one of the minimum percentages of the contrast MTF _A at the percentage of the image height H _A is defined. However, a plurality of percentages of the contrast MTF at a plurality of percentages of the image height H may be defined.

FIG. 16 illustrates the first graph of the distortion curve DC and the second graph of the MTF curve MC of the optical lens 40 of the imaging device 20 in a case where two minimum percentages of the contrast MTF are defined in the MTF curve MC. FIG. 17 shows conditions which the distortion curves DC and the MTF curve MC represented in FIG. 16 should satisfy. FIG. 16 and FIG. 17 correspond to FIG. 14 and FIG. 15 mentioned above, respectively.

The first graph of the distortion curve DC in FIG. 16 is the same as that in FIG. 14. The second graph of the MTF curve MC is the same as that in FIG. 14 except that a minimum percentage of the contrast MTF ₁₀₀ at 100 percent of the image height H ₁₀₀ is also defined.

For the distortion curve DC and the MTF curve MC represented in FIG. 16, the condition 1 through the condition 4 in FIG. 17 are the same as those in FIG. 15. However, the condition 5 in FIG. 17 is different from that in FIG. 15.

As shown in FIG. 16 and FIG. 17, in the second graph of the percentage of the contrast MTF, an MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X 9 X MTF ₀. Here, the MTF _A is the X-coordinate of the MTF curve MC in the second graph when the percentage of the image height H is H _A. As defined in the condition 3, the H _A is a Y-coordinate of the intersection point of the first linear line L1 and the second linear line L2 of the distortion curve DC in the first graph, and the distortion ratio D ₁₀₀ is the distortion ratio D at 100 percent of the image height H ₁₀₀. The MTF ₀ is the percentage of the contrast MTF when the percentage of the image height H ₀ is 0. 9 is a coefficient Co to adjust a minimum percentage of the contrast MTF _A at the percentage of the image height H _A. That is, 9 is just an example of the coefficient Co to adjust the minimum percentage of the contrast MTF _A.

Similarly, in the second graph of the percentage of the contrast MTF, an MTF ₁₀₀ is equal to or greater than the distortion ratio D ₁₀₀ X 7 X MTF ₀. Here, the MTF ₁₀₀ is the X-coordinate of the MTF curve MC in the second graph at the percentage of the image height H is 100 percent. In other words, the MTF ₁₀₀ is the percentage of the contrast MTF when the percentage of the image height H ₁₀₀ is 100.7 is a coefficient Co ₁₀₀ to adjust a minimum percentage of the contrast MTF ₁₀₀ at the percentage of the image height H ₁₀₀. That is, 7 is just an example of the coefficient Co ₁₀₀ to adjust the minimum percentage of the contrast MTF ₁₀₀.

For example, if the distortion ratio D ₁₀₀ is 8 percent (0.08) , then the MTF _A is equal to or greater than 0.08 X 9 X MTF ₀ = 0.72 X MTF ₀ and the MTF ₁₀₀ is equal to or greater than 0.08 X 7 X MTF ₀ = 0.56 X MTF ₀.

That is, the condition 5 defines that 72 percent of the MTF ₀ is the lowest value for the MTF _A and 56 percent of the MTF ₀ is the lowest value for the MTF ₁₀₀. It is noted that, since the maximum distortion ration D ₁₀₀ is 10 percent in the condition 4, the coefficients Co and Co ₁₀₀ have to be less than 10 in the condition 5 and therefore Co=9 and Co ₁₀₀=7 are allowable values.

If the MTF curve MC satisfies the condition 5, the contrast of the center part of the object image can be sharp. Moreover, the sharpness of the peripheral part of the object image, which is outside the center part of the object image, can still be maintained. Generally, the contrast of the object image at the image height H ₁₀₀ is worst throughout the object image. Therefore, by defining the minimum percentage of the contrast MTF ₁₀₀ at the image height H ₁₀₀, a certain level of sharpness of the entire object image can be guaranteed.

Although two percentages of the contrast MTF _A and MTF ₁₀₀ are defined in the example of the MTF curve MC in FIG. 16, three, four, or more percentages of the contrast MTF may be defined. That is, one ore more percentages of the contrast MTF can be defined in the optical lens 40 of the imaging device 20 in the condition 5 according to the present embodiment.

In addition, although the distortion curve DC is linearized and approximated by two linear lines, i.e., the first liner line L1 and the second linear line L2 in FIG. 14 and FIG. 16, the distortion curve DC may be linearized and approximated by three linear lines, four linear lines, or more.

FIG. 18 illustrates the distortion curve DC in the first coordinate system and the MTF curve MC in the second coordinate system of the optical lens 40 of the imaging device 20 according to a modification of the present embodiment. In FIG. 18, the distortion curve DC is linearized and approximated by three lines, i.e., the first linear line L1 and the second linear line L2 as well as a third linear line L3.

The first linear line L1 approximates a lower part of the distortion curve DC, the second linear line L2 approximates a middle part of the distortion curve DC, and the third linear line L3 approximates a higher part of the distortion curve DC.

Also in this example shown in FIG. 18, the distortion curve DC and the MTF curve MC may satisfy all of the condition 1 through the condition 5 or satisfy any combinations of the condition 1 through the condition 5 shown in FIG. 17.

For example, the angle α ₁ is greater than the angle α ₂ in the condition 2, where the angle α ₁ is the angle formed by the first linear line L1 and the X-axis of the first coordinate system and the angle α ₂ is the angle formed by the second linear line L2 and the X-axis of the first coordinate system.

Moreover, in the MTF curve in the second coordinate system, the MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X 9 X MTF ₀ in the condition 5 in FIG. 17. Here, the H _A is also the Y-coordinate of the intersection point of the first linear line L1 and the second linear line L2 of the distortion curve DC, and the MTF _A is also the X-coordinate of the MTF curve MC when the percentage of the image height H is H _A. That is, the MTF _A is the percentage of the contrast MTF when the percentage of the image height H is H _A.

Incidentally, as mentioned above, the optical lens 40 may be composed of one lens element or a combination of a plurality of lens elements.

FIG. 19 illustrates an internal structure of the optical lens 40. As shown in FIG. 19, the optical lens 40 includes at least one lens element 42 and a casing 44 to accommodate the lens element 42. In other words, the optical lens 40 may have one lens element 42. Alternatively, the optical lens 40 may have a combination of a plurality of the lens elements 42. The casing 44 supports at least one lens element 42 and maintains an optical performance of the lens element 42.

In order to manufacture the optical lens 40, the lens element 42 is provided as well as the casing 44 is provided. Thereafter, the lens element 42 and the casing 44 are assembled into the optical lens 40. That is, the casing 44 accommodates the lens element 42 when assembled.

As explained herein above, in accordance with the imaging device 20 of the electrical device 10 of the present embodiment, since the focal length f' can be shortened, the height H _imd of the imaging device 20 can be reduced. Therefore, a thickness of the electrical device 10 including the imaging device 20 can be also reduced.

Also, since the height H _imd of the imaging device 20 can be lowered, a projection part for the imaging device 20 of the electrical device 10 can be eliminated and a thin and slim electrical device 10 can be realized. In other words, a full flat surface of the electrical device 10 can be designed.

In addition, even if a larger size of the imaging sensor 50 is employed, the height H _imd of the imaging device 20 can be still reduced because the focal length f' can be shortened as compared to the conventional imaging device. Therefore, the larger size of the imaging sensor 50 can be equipped with the electrical device 10 and a quality of the object image and the final target image can be raised.

In the description of embodiments of the present disclosure, it is to be understood that terms such as "central" , "longitudinal" , "transverse" , "length" , "width" , "thickness" , "upper" , "lower" , "front" , "rear" , "left" , "right" , "vertical" , "horizontal" , "top" , "bottom" , "inner" , "outer" , "clockwise" and "counterclockwise" should be construed to refer to the orientation or the position as described or as shown in the drawings under discussion. These relative terms are only used to simplify description of the present disclosure, and do not indicate or imply that the device or element referred to must have a particular orientation, or constructed or operated in a particular orientation. Thus, these terms cannot be constructed to limit the present disclosure.

In addition, terms such as "first" and "second" are used herein for purposes of description and are not intended to indicate or imply relative importance or significance or to imply the number of indicated technical features. Thus, the feature defined with "first" and "second" may comprise one or more of this feature. In the description of the present disclosure, "a plurality of" means two or more than two, unless specified otherwise.

In the description of embodiments of the present disclosure, unless specified or limited otherwise, the terms "mounted" , "connected" , "coupled" and the like are used broadly, and may be, for example, fixed connections, detachable connections, or integral connections; may also be mechanical or electrical connections ; may also be direct connections or indirect connections via intervening structures; may also be inner communications of two elements, which can be understood by those skilled in the art according to specific situations.

In the embodiments of the present disclosure, unless specified or limited otherwise, a structure in which a first feature is "on" or "below" a second feature may include an embodiment in which the first feature is in direct contact with the second feature, and may also include an embodiment in which the first feature and the second feature are not in direct contact with each other, but are contacted via an additional feature formed therebetween. Furthermore, a first feature "on" , "above" or "on top of" a second feature may include an embodiment in which the first feature is right or obliquely "on" , "above" or "on top of" the second feature, or just means that the first feature is at a height higher than that of the second feature; while a first feature "below" , "under" or "on bottom of" a second feature may include an embodiment in which the first feature is right or obliquely "below" , "under" or "on bottom of" the second feature, or just means that the first feature is at a height lower than that of the second feature.

Various embodiments and examples are provided in the above description to implement different structures of the present disclosure. In order to simplify the present disclosure, certain elements and settings are described in the above. However, these elements and settings are only by way of example and are not intended to limit the present disclosure. In addition, reference numbers and/or reference letters may be repeated in different examples in the present disclosure. This repetition is for the purpose of simplification and clarity and does not refer to relations between different embodiments and/or settings. Furthermore, examples of different processes and materials are provided in the present disclosure. However, it would be appreciated by those skilled in the art that other processes and/or materials may be also applied.

Reference throughout this specification to "an embodiment" , "some embodiments" , "an exemplary embodiment" , "an example" , "a specific example" or "some examples" means that a particular feature, structure, material, or characteristics described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the above phrases throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Any process or method described in a flow chart or described herein in other ways may be understood to include one or more modules, segments or portions of codes of executable instructions for achieving specific logical functions or steps in the process, and the scope of a preferred embodiment of the present disclosure includes other implementations, in which it should be understood by those skilled in the art that functions may be implemented in a sequence other than the sequences shown or discussed, including in a substantially identical sequence or in an opposite sequence.

The logic and/or step described in other manners herein or shown in the flow chart, for example, a particular sequence table of executable instructions for realizing the logical function, may be specifically achieved in any computer readable medium to be used by the instruction execution system, device or equipment (such as the system based on computers, the system comprising processors or other systems capable of obtaining the instruction from the instruction execution system, device and equipment and executing the instruction) , or to be used in combination with the instruction execution system, device and equipment. As to the specification, "the computer readable medium" may be any device adaptive for including, storing, communicating, propagating or transferring programs to be used by or in combination with the instruction execution system, device or equipment. More specific examples of the computer readable medium comprise but are not limited to: an electronic connection (an electronic device) with one or more wires, a portable computer enclosure (a magnetic device) , a random access memory (RAM) , a read only memory (ROM) , an erasable programmable read-only memory (EPROM or a flash memory) , an optical fiber device and a portable compact disk read-only memory (CDROM) . In addition, the computer readable medium may even be a paper or other appropriate medium capable of printing programs thereon, this is because, for example, the paper or other appropriate medium may be optically scanned and then edited, decrypted or processed with other appropriate methods when necessary to obtain the programs in an electric manner, and then the programs may be stored in the computer memories.

It should be understood that each part of the present disclosure may be realized by the hardware, software, firmware or their combination. In the above embodiments, a plurality of steps or methods may be realized by the software or firmware stored in the memory and executed by the appropriate instruction execution system. For example, if it is realized by the hardware, likewise in another embodiment, the steps or methods may be realized by one or a combination of the following techniques known in the art: a discrete logic circuit having a logic gate circuit for realizing a logic function of a data signal, an application-specific integrated circuit having an appropriate combination logic gate circuit, a programmable gate array (PGA) , a field programmable gate array (FPGA) , etc.

Those skilled in the art shall understand that all or parts of the steps in the above exemplifying method of the present disclosure may be achieved by commanding the related hardware with programs. The programs may be stored in a computer readable storage medium, and the programs comprise one or a combination of the steps in the method embodiments of the present disclosure when run on a computer.

In addition, each function cell of the embodiments of the present disclosure may be integrated in a processing module, or these cells may be separate physical existence, or two or more cells are integrated in a processing module. The integrated module may be realized in a form of hardware or in a form of software function modules. When the integrated module is realized in a form of software function module and is sold or used as a standalone product, the integrated module may be stored in a computer readable storage medium.

The storage medium mentioned above may be read-only memories, magnetic disks, CD, etc.

Although embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that the embodiments are explanatory and cannot be construed to limit the present disclosure, and changes, modifications, alternatives and variations can be made in the embodiments without departing from the scope of the present disclosure.

Claims

An optical lens comprising at least one lens element and a casing to accommodate the lens element, wherein an object to be imaged is located at a first side of the optical lens and an imaging sensor to capture an object image of the object is located at a second side of the optical lens, the second side of the optical lens being an opposite side of the first side of the optical lens, wherein

a distortion curve of the optical lens represented in a first coordinate system is linearized by at least a first linear line and a second linear line, wherein an X-axis of the first coordinate system is a distortion ratio D and a Y-axis of the first coordinate system is a percentage of an image height H of the object image on the imaging sensor,

the first linear line approximates a lower part of the image height of the distortion curve in the first coordinate system and the second linear line approximates a higher part of the image height of the distortion curve in the first coordinate system,

an angle α ₁ is greater than an angle α ₂, where the angle α ₁ is an angle formed by the first linear line and the X-axis of the first coordinate system, and the angle α ₂ is an angle formed by the second linear line and the X-axis of the first coordinate system,

an MTF (Modulation Transfer Function) curve of the optical lens is represented in a second coordinate system, wherein an X-axis of the second coordinate system is a percentage of a contrast MTF, and a Y-axis of the second coordinate system is the percentage of the image height H of the object image on the imaging sensor, and

the optical lens satisfies a condition that an MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X Co X MTF ₀, where

the MTF _A is an X-coordinate of the MTF curve in the second coordinate system when the percentage of the image height H is H _A,

the H _A is a Y-coordinate of an intersection point of the first linear line and the second linear line of the distortion curve in the first coordinate system,

the distortion ratio D ₁₀₀ is the distortion ratio D at 100 percent of the image height H ₁₀₀,

the MTF ₀ is the percentage of the contrast MTF when the percentage of the image height H ₀ is 0, and

the Co is a coefficient to adjust a minimum percentage of the contrast MTF _A.
The optical lens according to claim 1, wherein the coefficient Co is 10.
The optical lens according to claim 1, wherein the MTF curve in the second coordinate system is described based on a 1/4 Nyquist frequency.
The optical lens according to claim 3, wherein the MTF curve in the second coordinate system is described based on a tangential orientation.
The optical lens according to claim 1, wherein the optical lens further satisfies a condition that an MTF ₁₀₀ is equal to or greater than the distortion ratio D ₁₀₀ X Co ₁₀₀ X MTF ₀, where

the MTF ₁₀₀ is the percentage of the contrast MTF when the percentage of the image height H ₁₀₀ is 100, and

the Co ₁₀₀ is a coefficient to adjust a minimum percentage of the contrast MTF ₁₀₀ at 100 percent of the image height H ₁₀₀.
The optical lens according to claim 5, wherein the coefficient Co is 9 and the coefficient Co ₁₀₀ is 7.
An imaging device, comprising:

the optical lens according to any one of the claims 1-6; and

the imaging sensor, on which the optical lens forms the object image.
The imaging device according to claim 7, wherein a position of 100 percent of an image height H ₁₀₀ of the object image is located at a corner of the imaging sensor.
The imaging device according to claim 7, wherein the object image on the imaging sensor is subjected to a distortion correction process to generate a final target image.
The imaging device according to claim 8, wherein the optical lens generates a pincushion distortion,

an edge of the final target image is decided based on the corner of the object image at the corner of the imaging sensor, and

an outside region of the object image which is outside the final target image is cut out when the final target image is generated.
The imaging device according to claim 8, wherein a distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ of the object image of the optical lens is equal to or greater than 5 percent and equal to or less than 10 percent.
The imaging device according to claim 11, wherein the percentage of the image height H _A is equal to or greater than 20 percent and equal to or less than 50 percent.
An electrical device, comprising:

the imaging device according to any one of claims 7-12; and

a distortion correction processor configured to execute the distortion correction process to correct a distortion of the object image on the imaging sensor to generate the final target image.
A method of manufacturing an optical lens, comprising:

providing a casing;

providing at least one lens element;

assembling the casing and the lens element into the optical lens so that an object to be imaged is located at a first side of the optical lens and an imaging sensor to capture an object image of the object is located at a second side of the optical lens, the second side of the optical lens being an opposite side of the first side of the optical lens, wherein

a distortion curve of the optical lens represented in a first coordinate system is linearized by at least a first linear line and a second linear line, wherein an X-axis of the first coordinate system is a distortion ratio D and a Y-axis of the first coordinate system is a percentage of an image height H of the object image on the imaging sensor,

the first linear line approximates a lower part of the image height of the distortion curve in the first coordinate system and the second linear line approximates a higher part of the image height of the distortion curve in the first coordinate system,

an angle α ₁ is greater than an angle α ₂, where the angle α ₁ is an angle formed by the first linear line and the X-axis of the first coordinate system, and the angle α ₂ is an angle formed by the second linear line and the X-axis of the first coordinate system,

an MTF (Modulation Transfer Function) curve of the optical lens is represented in a second coordinate system, wherein an X-axis of the second coordinate system is a percentage of a contrast MTF, and a Y-axis of the second coordinate system is the percentage of the image height H of the object image on the imaging sensor, and

the optical lens satisfies a condition that an MTF _A is equal to or greater than the distortion ratio D ₁₀₀ X Co X MTF ₀, where

the MTF _A is an X-coordinate of the MTF curve in the second coordinate system when the percentage of the image height H is H _A,

the H _A is a Y-coordinate of an intersection point of the first linear line and the second linear line of the distortion curve in the first coordinate system,

the distortion ratio D ₁₀₀ is the distortion ratio D at 100 percent of the image height H ₁₀₀,

the MTF ₀ is the percentage of the contrast MTF when the percentage of the image height H ₀ is 0, and

the Co is a coefficient to adjust a minimum percentage of the contrast MTF _A.
The method according to claim 14, wherein the coefficient Co is 10.
The method according to claim 14, wherein the MTF curve in the second coordinate system is described based on a 1/4 Nyquist frequency.
The method according to claim 16, wherein the MTF curve in the second coordinate system is described based on a tangential orientation.
The method according to claim 14, wherein the optical lens further satisfies a condition that an MTF ₁₀₀ is equal to or greater than the distortion ratio D ₁₀₀ X Co ₁₀₀ X MTF ₀, where

the MTF ₁₀₀ is the percentage of the contrast MTF when the percentage of the image height H ₁₀₀ is 100, and

the Co ₁₀₀ is a coefficient to adjust a minimum percentage of the contrast MTF ₁₀₀ at 100 percent of the image height H ₁₀₀.
The method according to claim 18, wherein the coefficient Co is 9 and the coefficient Co ₁₀₀ is 7.
A method of manufacturing an imaging device, comprising:

providing a support member;

providing the optical lens according to any one of the claims 14-19;

providing the imaging sensor; and

assembling the support member, the optical lens and the imaging sensor into the imaging device.
The method according to claim 20, wherein a position of 100 percent of an image height H ₁₀₀ of the object image is located at a corner of the imaging sensor.
The method according to claim 20, wherein the object image on the imaging sensor is subjected to a distortion correction process to generate a final target image.
The method according to claim 21, wherein the optical lens generates a pincushion distortion,

an edge of the final target image is decided based on the corner of the object image at the corner of the imaging sensor, and

an outside region of the object image which is outside the final target image is cut out when the final target image is generated.
The method according to claim 21, wherein a distortion ratio D ₁₀₀ at 100 percent of the image height H ₁₀₀ of the object image of the optical lens is equal to or greater than 5 percent and equal to or less than 10 percent.
The method according to claim 24, wherein the percentage of the image height H _A is equal to or greater than 20 percent and equal to or less than 50 percent.
A method of manufacturing an electrical device, comprising:

providing the imaging device according to any one of claims 20-25;

providing a distortion correction processor configured to execute the distortion correction process to correct a distortion of the object image on the imaging sensor to generate the final target image; and

assembling the imaging device and the distortion correction processor into the electrical device.