WO2023010239A1

WO2023010239A1 - Zoom lens optical system

Info

Publication number: WO2023010239A1
Application number: PCT/CN2021/110020
Authority: WO
Inventors: Sota Miyatani; Qing TONG; Takuya Anzawa; Ryotaro Izumi; Kazuya Atsuta
Original assignee: Huawei Technologies Co.,Ltd.
Priority date: 2021-08-02
Filing date: 2021-08-02
Publication date: 2023-02-09
Also published as: CN117916644A

Abstract

A switching zoom lens comprises, from an object side to an image side along an optical axis (OA), a reflective optical element (P) to bend an optical path from the object side to the image side, a front lens group (Gf) with a positive refractive power, and a rear lens group (Gr) comprising three or more and five or less lens elements (L7-L10). When zooming from a wide angle end to a telephoto end, the rear lens group (Gr) is inserted between the front lens group (Gf) and an imaging surface (IMG), and when zooming from the telephoto end to the wide angle end, the rear lens group (Gr) is moved out of the optical path of the switching zoom lens.

Description

ZOOM LENS OPTICAL SYSTEM

FIELD OF THE DISCLOSURE

The present disclosure relates to an image pickup lens that forms an object image for a solid-state image sensor such as a CCD or CMOS sensor, and more particularly to a portable device represented by a smartphone, a game machine, a PC, an IP camera, a home appliance, an automobile, or an unmanned aircraft. The present disclosure relates to an image pickup lens and an imaging device mounted on the camera and the like.

BACKGROUND OF THE DISCLOSURE

With the popularization of smartphones in recent years, the needs for imaging lenses have diversified, and it is desired to improve the optical performance such as a wider view-angle, higher telephoto performance, and larger diameter (higher NA) while maintaining the size of an imaging module that is directly affected by the product size. Nowadays, given that multi-camera systems have become mainstream, wide-angle lenses play a major role in measuring differentiation in smartphone products since wide-angle lenses are often used for still image and motion picture shooting of distant subjects such as sports event, landscapes and astronomical observation.

As an optical system used for such a telephoto lens module, a periscope type using a right-angle prism is currently used for smartphones in consideration of lowering the height of the module. However, in most cases at present, this periscope type for telephoto has a fixed focus, and it only shoots one fixed angle of view. Therefore, when telephoto shooting is desired, the digital image is often cut out and up-converted by digital zoom, which causes a problem of image quality deterioration.

A zoom lens system can be considered to solve this problem. However, when a zoom optical system having a lens group moving along the optical axis for zooming is applied, as the zoom magnification increases, the movement distance of the lens group for zooming becomes long, which is a major factor leading to an increase in the size and cost for a small lens module for smartphones, etc. As an example of a periscope type zoom lens, there is a prior art in which the optical axis is moved, but in this case, the lens moving distance when the magnification ratio is doubled becomes as long as about 6 mm.

In order to solve aforementioned problem, the image pickup lens according to the present disclosure optically switches the angle of view between telephoto and wide-angle without changing the total track length (TTL) .

SUMMARY OF THE DISCLOSURE

The present disclosure mitigates and/or obviates the aforementioned disadvantages.

The primary objective of the present disclosure is to provide a lens which has a size that can be mounted on a mobile device, and which optically switches the angle of view between telephoto and wide-angle without changing the TTL.

According to a first aspect, a switching zoom lens is provided. The switching zoom lens comprises, from an object side to an image side along an optical axis, a reflective optical element to bend an optical path from the object side to the image side, a front lens group with a positive refractive power, and a rear lens group comprising three or more and five or less lens elements. When zooming from a wide angle to a telephoto, the rear lens group is inserted between the front lens group and an imaging surface, and when zooming from the telephoto end to the wide angle end, the rear lens group is moved out of an optical path of the switching zoom lens.

This switching is actuated by a switching mechanism powered by a piezo element, a VCM, or the like.

High accuracy of all positions on the optical axis from the wide-angle end to the telephoto end is required for a conventional zoom lens, and high holding accuracy of multiple positions on the optical axis is required for a two-focus zoom lens. Thus, compared to such conventional zoom lens and two-focus zoom lens, the switching zoom lens of the present disclosure only needs to ensure the positional accuracy when the rear lens group Gr is inserted into the optical path, so it can be said that the amount of deterioration in the optical performance is less than that of conventional lenses and it is easier to perform quick zooming.

It is also an advantage that the holding accuracy of the rear lens group Gr in this telephoto state can be achieved by a relatively inexpensive method such as an offset mechanism. Switching mechanisms may include a mechanism that repeats insertion and removal linearly while maintaining the same posture of the rear lens group Gr, and a pendulum mechanism that actuates changing the angle of the optical axis of the rear lens group Gr when inserting and removing the rear lens group Gr.

By using such a switching zoom lens module, it is possible to provide high-speed optical magnification change while avoiding the use of a mechanism and an expensive zoom motor for a large amount of movement of a lens group for zooming.

The switching zoom lens can be configured as a periscope type by bending the optical path from the object with the reflecting optical element. The periscope type is advantageous for reducing the height of the lens module. The reflecting optical element can be omitted, but since the telephoto type lens module has a long overall length, the thickness tends to increase in the direction in which the lens (camera) is directed.

If the rear lens group has less than three lens elements, the aberration correction power in the telephoto state is insufficient and the resolution performance deteriorates. If the rear lens group has more than five lens elements, the weight and the volume of the rear lens group increase whichcauses the load at the time of insertion and removal to increase, and this also presents problems such as the need to take a large space for evacuation in the wide-angle state.

According to one aspect of the present switching zoom lens system, when ft is a focal length of the switching zoom lens in the telephoto state, fw is a focal length of the zoom lens in the wide-angle state, and FOVw is the field of view of the switching zoom lens in the wide-angle state, the following conditions are satisfied:

(i) 1.2 ≤ ft/fw ≤ 3; and

(ii) 16.5° ≤ FOVw ≤ 28.5°.

The condition (i) defines the zoom ratio between the wide-angle state and the telephoto state. If the zoom ratio is below the lower limit of the range, it is easier to design the lens, but the zoom ratio is too small to provide a desired user experience. If the zoom ratio exceeds the upper limit of the range, the user would appreciate the large zoom ratio, but the F number becomes too large due to the characteristics of the optical system called the periscope type wherein the aperture is limited, which causes deterioration of resolution performance due to diffraction limit. Moreover, when the zoom ratio becomes large, the amount of movement of the front lens group required to change the magnification increases. This makes it difficult to solve the problem of the present disclosure of keeping the moving distance of the lens group small when zooming, and suppressing the motor size and cost.

Alternatively, the following conditions are satisfied:

(i) -2 1.25 ≤ ft/fw ≤ 2.5; and

(ii) -2 18.5° ≤ FOVw ≤ 26.5°.

The condition (ii) defines the angle of view in the wide-angle state. If the angle of view is below the lower limit of the range, the angle of view in the wide-angle state becomes too narrow to be considered wide-angle. Conversely, if the angle of view exceeds the upper limit of the range, the angle of view in the wide-angle state becomes too large as a periscope type system. Specifically, vignetting occurs at the peripheral angle of view on the reflective optical element.

According to one aspect of the present switching zoom lens system, when X is a zoom ratio of the switching zoom lens as expressed by X=0.3* (ft/fw-1) , and Fgd is an absolute value of the amount of movement of the front lens group along the optical axis when zooming from the wide angle end to the telephoto end, the following condition is satisfied:

(iii) X -0.2 ≤ Fgd/fw ≤ X +0.2.

The condition (iii) defines a range of movement of the front lens group that is appropriate for the zoom ratio. If the range of movement is below the lower limit of the range, the moving distance of the front lens group during zooming is kept small, but zooming by inserting the rear lens group and aberration correction in the telephoto state cannot be performed at the same time, and the desired zoom ratio cannot be obtained, or the desired imaging performance cannot be obtained. If the range of movement exceeds the upper limit of the range, it becomes easier to obtain the zoom ratio and the imaging performance, but it becomes difficult to keep the moving distance of the lens from becoming too long when zooming. This makes it difficult to solve the problem of the present disclosure of keeping the moving distance of the lens group small when zooming, and suppressing the motor size and cost.

Alternatively, the following condition is satisfied:

(iii) X -0.1 ≤ Fgd/fw ≤ X +0.1.

According to one aspect of the present switching zoom lens system, the most object side lens in the front lens group satisfies the following condition, when fLo is a focal length of the most object side lens of the front lens group:

(iv) 0.5 ≤ fLo/fw ≤ 1.2.

The condition (iv) defines the refractive power of the most image side lens of the front lens group in an appropriate range. If the refractive power is below the lower limit, the refractive power of the most image side lens becomes too large, and it becomes difficult to correct aberrations in the telephoto state where the rear group is inserted, and the desired resolution performance cannot be obtained. There is also a problem in that the distance from the most image side lens to the imaging surface tends to be too short with respect to the focal length in the wide-angle state and exceeds the upper limit of the condition (iii) . If the refractive power exceeds the upper limit of the range, it becomes easier to obtain the desired resolution performance in the telephoto state and satisfy the condition (iii) , but there is a problem in that the total length of the lens module itself becomes too long.

Alternatively, the following condition is satisfied:

(iii) -2 0.65 ≤ fLo/fw ≤ 1.05

According to one aspect of the present switching zoom lens system, focusing is performed by moving the front lens group along the optical axis in both the wide-angle state and the telephoto state.

Therefore, focusing is available with or without the rear lens group, in other words, in both the wide-angle state and the telephoto state.

According to one aspect of the present switching zoom lens system, the most image side lens of the front lens group has a negative refractive power, and the following condition is satisfied when fLi is a focal length of the most image side lens of the front lens group:

(v) fLi/fw ≤ -0.5.

The condition (v) defines an appropriate range for the refractive power of the most image side lens in the front lens group. If the refractive power exceeds the upper limit, the angle of light rays emitted from the front lens group toward the rear lens group tends to increase, and there is a problem in that aberration correction in the telephoto state is not sufficiently achieved and the desired resolution performance cannot be obtained.

Alternatively, the following condition is satisfied:

(v) -2 fLi/fw ≤ -0.7.

According to a second aspect, a camera is provided. The camera comprises the wide-angle lens optical system provided in the first aspect and an image sensor. The wide-angle lens optical system is configured to input light, which is used to carry image data, to the image sensor, and the image sensor is configured to display an image according to the image data.

According to a third aspect, a terminal is provided. The terminal comprises a camera, which is the camera provided in the second aspect, and a Graphic Processing Unit (GPU) . The GPU is connected to the camera. The camera is configured to obtain image data and input the image data into the GPU, and the GPU is configured to process the image data received from the camera. The terminal can be applied to small cameras for mobile devices such as mobile phones and tablets.

The present disclosure will be presented in further detail based on the following descriptions with accompanying drawings, which show, for the purpose of illustration only, the preferred embodiments in accordance with the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood from the following detailed description of non-limiting embodiments thereof, and on examining the accompanying drawings, in which:

FIG 1-1 shows a cross-sectional illustration of a switching zoom lens in accordance with a first embodiment of the present disclosure in the wide-angle state.

FIG 1-2 shows a cross-sectional illustration of the switching zoom lens in accordance with the first embodiment of the present disclosure in the telephoto state.

FIG 1-3 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the first embodiment of the present disclosure in the wide-angle state.

FIG 1-4 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the first embodiment of the present disclosure in the telephoto state.

FIG 2-1 shows a cross-sectional illustration of a switching zoom lens in accordance with a second embodiment of the present disclosure in the wide-angle state.

FIG 2-2 shows a cross-sectional illustration of the switching zoom lens in accordance with the second embodiment of the present disclosure in the telephoto state.

FIG 2-3 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the second embodiment of the present disclosure in the wide-angle state.

FIG 2-4 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the second embodiment of the present disclosure in the telephoto state.

FIG 3-1 shows a cross-sectional illustration of a switching zoom lens in accordance with a third embodiment of the present disclosure in the wide-angle state.

FIG 3-2 shows a cross-sectional illustration of the switching zoom lens in accordance with the third embodiment of the present disclosure in the telephoto state.

FIG 3-3 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the third embodiment of the present disclosure in the wide-angle state.

FIG 3-4 shows a longitudinal spherical aberration, an astigmatic field curve, and a distortion of the switching zoom lens in accordance with the third embodiment of the present disclosure in the telephoto state.

FIG 4 shows an implementation of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments of a switching zoom lens system of the present disclosure will be described with reference to the figures and optical data. This switching zoom lens system can be applied to small cameras for mobile devices such as a mobile phones and tablets.

The switching zoom lens according to the present disclosure comprises, in order from an object side, a reflective optical element to bend an optical path from the object side to the image side, a front lens group, and a rear lens group. When zooming from a wide-angle end to a telephoto end, the rear lens group is inserted between the front lens group and an imaging surface, and when zooming from the telephoto end to the wide-angle end, the rear lens group is moved out of an optical path of the switching zoom lens. The switching zoom lens can be mounted on a mobile device and optically switches the angle of view between telephoto and wide-angle without changing the TTL.

First Embodiment

FIG 1-1 shows a cross-sectional illustration of a switching zoom lens system in accordance with a first embodiment of the present disclosure in the wide-angle state.

The switching zoom lens system comprises a reflective optical element P to bend an optical path from the object side to the image side, a front lens group Gf with a positive refractive power, and a rear lens group Gr. The front lens group Gf comprises a first lens element L1, a second lens element L2, a third lens element L3, a fourth lens element L4, a fifth lens element L5, and a sixth lens element L6. The rear lens group Gr comprises a seventh lens element L7, an eighth lens element L8, a ninth lens element L9, and a tenth lens element L10. An optical filter IR such as an infrared cut filter or a cover glass may be arranged on an imaging surface IMG. The optical filter IR can be omitted.

FIG 1-1 does not show the rear lens group Gr because, in the wide-angle state, the rear lens group Gr is removed in the direction perpendicular to the optical axis in a front/back direction of FIG 1-1 and FIG 1-2, such that the movement of the rear lens group Gr does not increase the thickness, i.e., in the up/down direction of the figures. When switching to the telephoto state, the rear group Gr moves on the optical path and stands still with the optical axis of the rear lens group Gr aligned with the optical axis OA of the switching zoom lens.

FIG 1-2 shows a cross-sectional illustration of the switching zoom lens system in accordance with the first embodiment of the present disclosure in the telephoto state. For the telephoto state, the front lens group Gf is moved towards the object side along the optical axis OA, and the rear lens group Gr is moved into the optical path between the front lens group Gf and the imaging surface perpendicularly to the optical axis OA such that the front lens group Gr is arranged about the optical axis OA.

The rear lens group Gr is removed out of the optical path perpendicularly to the optical axis OA, and the front lens group Gf is moved towards the image side along the optical axis OA back to the wide-angle state. In other words, the rear lens group Gr is not used in the wide-angle state.

Further, the movement when the rear lens group Gr is removed to the wide-angle state from the telephoto state does not have to be perpendicular to the optical axis of the switching zoom lens. Since the wide-angle rear lens group Gr is not involved in imaging in the wide-angle state, the rear lens group Gr may also be removed in any fashion as long as it is completely out of the optical path.

The front lens group Gf is also used for focusing by moving along the optical path OA for both the wide-angle state and the telephoto state.

In this way, the switching zoom lens of the present disclosure can quickly zoom in and out between the wide-angle state and the telephoto state, and the zooming mechanism can be easily designed.

Table 1-1 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the first embodiment in the wide-angle state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric. Note that the lens elements L7 to L10 are not on this table since the rear lens group Gr is not used in the wide-angle state.

Table 1-1

Table 1-2 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the first embodiment in the telephoto state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric.

Table 1-2

Table 1-3 shows the aspheric coefficients for each of the lens elements of the optical lens system in accordance with the first embodiment, wherein numbers 2, 4, …, 20 represent the higher order aspheric coefficients. The equation of the aspheric surface profiles is expressed as follows:

wherein:

z: the distance (sag amount) in the optical axis direction from the apex of the lens surface;

H: the height in the direction perpendicular to the optical axis direction;

c: paraxial curvature at the apex of the lens (reciprocal of radius of curvature) ;

Y: the distance from a point on the curve of the aspheric surface to the optical axis;

k: the conic coefficient; and

Ai: the aspheric coefficient of order i.

Table 1-3

Aspheric Coefficient

FIG 1-3 shows a longitudinal spherical aberration for each wavelength, an astigmatic field curve where the amount of d-line aberration on the sagittal image plane S is shown by a solid line and the amount of d-line aberration on the tangential image plane T is shown by a broken line, and a distortion where the amount of aberration on the d-line is shown by a solid line, of the switching zoom lens in accordance with the first embodiment of the present disclosure in the wide-angle state.

It can be seen from the diagrams that each aberration is satisfactorily corrected.

Second Embodiment

FIG 2-1 shows a cross-sectional illustration of a switching zoom lens system in accordance with a second embodiment of the present disclosure in the wide-angle state.

FIG 2-1 does not show the rear lens group Gr because, in the wide-angle state, the rear lens group Gr is removed in the direction perpendicular to the optical axis in a front/back direction of FIG 2-1 and FIG 2-2, such that the movement of the rear lens group Gr does not increase the thickness, i.e., in the up/down direction of the figures. When switching to the telephoto state, the rear group Gr moves on the optical path and stands still with the optical axis of the rear lens group Gr aligned with the optical axis OA of the switching zoom lens.

FIG 2-2 shows a cross-sectional illustration of the switching zoom lens system in accordance with the second embodiment of the present disclosure in the telephoto state. For the telephoto state, the front lens group Gf is moved towards the object side along the optical axis OA, and the rear lens group Gr is moved into the optical path between the front lens group Gf and the imaging surface perpendicularly to the optical axis OA such that the front lens group Gr is arranged about the optical axis OA.

Table 2-1 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the second embodiment in the wide-angle state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric. Note that the lens elements L7 to L10 are not on this table since the rear lens group Gr is not used in the wide-angle state.

Table 2-1

Table 2-2 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the second embodiment in the telephoto state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric.

Table 2-2

Table 2-3 shows the aspheric coefficients for each of the lens elements of the optical lens system in accordance with the second embodiment, wherein numbers 2, 4, …, 20 represent the higher order aspheric coefficients.

Table 2-3

Aspheric Coefficient

FIG 2-3 shows a longitudinal spherical aberration for each wavelength, an astigmatic field curve where the amount of d-line aberration on the sagittal image plane S is shown by a solid line and the amount of d-line aberration on the tangential image plane T is shown by a broken line, and a distortion where the amount of aberration on the d-line is shown by a solid line, of the switching zoom lens in accordance with the second embodiment of the present disclosure in the wide-angle state.

Third Embodiment

FIG 3-1 shows a cross-sectional illustration of a switching zoom lens system in accordance with a third embodiment of the present disclosure in the wide-angle state.

The switching zoom lens system comprises a reflective optical element P to bend an optical path from the object side to the image side, a front lens group Gf with a positive refractive power, and a rear lens group Gr. The front lens group Gf comprises a first lens element L1, a third lens element L2, a third lens element L3, a fourth lens element L4, a fifth lens element L5, and a sixth lens element L6. The rear lens group Gr comprises a seventh lens element L7, an eighth lens element L8, a ninth lens element L9, and a tenth lens element L10. An optical filter IR such as an infrared cut filter or a cover glass may be arranged on an imaging surface IMG. The optical filter IR can be omitted.

FIG 3-2 shows a cross-sectional illustration of the switching zoom lens system in accordance with the third embodiment of the present disclosure in the telephoto state. For the telephoto state, the front lens group Gf is moved towards the object side along the optical axis OA, and the rear lens group Gr is moved into the optical path between the front lens group Gf and the imaging surface perpendicularly to the optical axis OA such that the front lens group Gr is arranged about the optical axis OA.

Table 3-1 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the third embodiment in the wide-angle state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric. Note that the lens elements L7 to L10 are not on this table since the rear lens group Gr is not used in the wide-angle state.

Table 3-1

Table 3-2 shows the radius of curvature and the thickness or separation for each of the optical surfaces, and the refractive index and the Abbe number with respect to the d line for each of the lens elements of the optical lens system in accordance with the third embodiment in the telephoto state. Opposite surfaces of each lens element are respectively referred to as surface S1 and surface S2 in order from the object side to the image side. Denotation “*” indicates that the surface is aspheric.

Table 3-2

Table 3-3 shows the aspheric coefficients for each of the lens elements of the optical lens system in accordance with the third embodiment, wherein numbers 2, 4, …, 20 represent the higher order aspheric coefficients.

Table 3-3

Aspheric Coefficient

FIG 3-3 shows a longitudinal spherical aberration for each wavelength, an astigmatic field curve where the amount of d-line aberration on the sagittal image plane S is shown by a solid line and the amount of d-line aberration on the tangential image plane T is shown by a broken line, and a distortion where the amount of aberration on the d-line is shown by a solid line, of the switching zoom lens in accordance with the third embodiment of the present disclosure in the wide-angle state.

It can be seen from the diagrams that each aberration is satisfactorily corrected. Further, with respect to the term used in the present disclosure, the refractive power refers to the refractive power in the paraxial axis (near the optical axis) .

As shown in the optical data above, the switching zoom lens system of the present disclosure is capable of providing a high-speed optical magnification change while avoiding the use of a mechanism and an expensive zoom motor for a large amount of movement of a lens group for zooming along the optical axis, and is also capable of achieving both high image quality and compactness. The switching zoom lens in these embodiments obtains a preferable effect by satisfying the following conditions:

(i) 1.2 ≤ ft/fw ≤ 3,

where ft is a focal length of the switching zoom lens in the telephoto state, and fw is a focal length of the switching zoom lens in the wide-angle state.

(ii) 16.5° ≤ FOVw ≤ 28.5°,

where FOVw is the field of view of the switching zoom lens in the wide-angle state.

(iii) X -0.2 ≤ Fgd/fw ≤ X +0.2,

where X is an zoom ratio between the wide-angle state and the telephoto state as expressed by X=0.3* (ft/fw-1) , and Fgd is an absolute value of the amount of movement of the front lens group along the optical axis when zooming from the wide angle end to the telephoto end.

(iv) 0.5 ≤ fLo/fw ≤ 1.2,

where fLo is a focal length of the most object side lens of the front lens group.

(v) fLi/fw ≤ -0.5,

where fLi is a focal length of the most image side lens of the front lens group.

The condition (i) defines the zoom ratio between the wide-angle state and the telephoto state. If the zoom ratio is below the lower limit of the range, it is easier to design the lens, but the zoom ratio is too small to provide a desired user experience. If the zoom ratio exceeds the upper limit of the range, the user would appreciate the large zoom ratio, but the F number becomes too large due to the characteristics of the optical system called the periscope type wherein the aperture is limited, which cause deterioration of resolution performance due to diffraction limit. Moreover, when the zoom ratio becomes large, the amount of movement of the front lens group required to change the magnification increases. This makes it difficult to solve the problem of the present disclosure of keeping the moving distance of the lens group small when zooming and suppressing the motor size and cost. From this viewpoint, the following condition may be selectively satisfied.

(i) -2 1.25 ≤ ft/fw ≤ 2.5

The condition (ii) defines the angle of view in the wide-angle state. If the angle of view is below the lower limit of the range, the angle of view in the wide-angle state becomes too narrow to be considered wide-angle. Conversely, if the angle of view exceeds the upper limit of the range, the angle of view in the wide-angle state becomes too large as a periscope type system. Specifically, vignetting occurs at the peripheral angle of view on the reflective optical element. From this viewpoint, the following condition may be selectively satisfied.

(ii) -2 18.5° ≤ FOVw ≤ 26.5°

The condition (iii) defines a range of movement of the front lens group that is appropriate for the zoom ratio. If the range of movement is below the lower limit of the range, the moving distance of the front lens group during zooming is kept small, but zooming by inserting the rear lens group and aberration correction in the telephoto state cannot be performed at the same time, and the desired zoom ratio cannot be obtained, or the desired imaging performance cannot be obtained. If the range of movement exceeds the upper limit of the range, it becomes easier to obtain the zoom ratio and the imaging performance, but it becomes difficult to keep the moving distance of the lens from becoming too long when zooming. This makes it difficult to solve the problem of the present disclosure of keeping the moving distance of the lens group small when zooming and suppressing the motor size and cost. From this viewpoint, the following condition may be selectively satisfied.

(iii) -2 X -0.1 ≤ Fgd/fw ≤ X +0.1

The condition (iv) defines the refractive power of the most image side lens of the front lens group in an appropriate range. If the refractive power is below the lower limit, the refractive power of the most image side lens becomes too large, and it becomes difficult to correct aberrations in the telephoto state where the rear group is inserted, and desired resolution performance cannot be obtained. There is also a problem that the distance from most image side lens to the imaging surface tends to be too short with respect to the focal length in the wide-angle state and exceed the upper limit of the condition (iii) . If the refractive power exceeds the upper limit of the range, it becomes easier to obtain the desired resolution performance in the telephoto state and satisfy the condition (iii) , but there is a problem in that the total length of the lens module itself becomes too long. From this viewpoint, the following condition may be selectively satisfied.

(iv) -2 0.65 ≤ fLo/fw ≤ 1.05

The condition (v) defines an appropriate range for the refractive power of the most image side lens in the front lens group. If the refractive power exceeds the upper limit, the angle of light rays emitted from the front lens group toward the rear lens group tends to increase, and there is a problem in that aberration correction in the telephoto state is not sufficiently achieved and the desired resolution performance cannot be obtained. From this viewpoint, the following condition may be selectively satisfied.

(v) -2 fLi/fw ≤ -0.7

Table 4 shows the values of the parameters used in the above-mentioned conditions from the first, second and third embodiments.

Table 4

parameter	Ex. 1	Ex. 2	Ex. 3
ft/fw	1.600	1.300	2.000
FOVw (°)	22.509	22.503	22.517
Fgd/fw	0.206	0.107	0.297
fLo/fw	0.766	0.962	0.853
fLi/fw	-0.890	-1.664	-1.846

By satisfying these conditions, the switching zoom lens of the present disclosure can be compact in a size that can be mounted on a mobile device, and can optically switch the angle of view between telephoto and wide-angle without changing the TTL. By using such a switching zoom lens module, it is possible to provide high-speed optical magnification change while avoiding the use of a mechanism and an expensive zoom motor for a large amount of movement of a lens group for zooming along the optical axis. The switching zoom lens can also be configured as a periscope type by bending the optical path from the object with the reflecting optical element. The periscope type is advantageous for reducing the height of the lens module.

Further, a camera is provided. The camera in the present disclosure comprises the switching zoom lens of the present disclosure and an image sensor. The switching zoom lens is configured to input light, which is used to project an image to the image sensor, and the image sensor is configured to convert the image into a digital image data.

FIG. 4 shows a terminal 1000 disclosed in the present disclosure. The terminal 1000 comprises a camera 100 provided in the above implementations and a Graphic Processing Unit (GPU) 200. The camera 100 is configured to convert an image through a switching zoom lens of the present disclosure to digital image data and input the digital image data into the GPU 200, and the GPU 200 is configured to process the image data received from the camera.

In FIG. 4, the terminal 1000 comprises two cameras 100. However, the terminal may comprise a single camera or more than two cameras and it (or they) could be connected to the single GPU 200. One of the cameras 100 can be combined with the switching zoom lens of the present disclosure, and the other camera 100 can be combined with a different type of lens such as a single focus wide-angle lens.

Although the lens system according to the present disclosure can be applied especially to mobile phone cameras, it can also be applied to cameras in any mobile device such as tablet-type devices and wearable devices

Although preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.

Claims

A switching zoom lens comprising, from an object side to an image side along an optical axis:

a reflective optical element to bend an optical path from the object side to the image side;

a front lens group with a positive refractive power; and

a rear lens group comprising three or more and five or less lens elements;

wherein, when zooming from a wide angle end to a telephoto end, the rear lens group is inserted between the front lens group and an imaging surface, and when zooming from the telephoto end to the wide angle end, the rear lens group is moved out of an optical path of the switching zoom lens, and

the following conditions are satisfied:

(i) 1.2 ≤ ft/fw ≤ 3; and

(ii) 16.5° ≤ FOVw ≤ 28.5°,

where ft is a focal length of the switching zoom lens in the telephoto state, fw is a focal length of the switching zoom lens in the wide-angle state, and FOVw is the field of view of the switching zoom lens in the wide-angle state.
The switching zoom lens as claimed in claim 1, wherein the following conditions are satisfied:

(i) -2 1.25 ≤ ft/fw ≤ 2.5; and

(ii) -2 18.5° ≤ FOVw ≤ 26.5°,
The switching zoom lens as claimed in in any of the claims 1-2, wherein the following condition is satisfied when zooming:

(iii) X -0.2 ≤ Fgd/fw ≤ X +0.2,

where X is a zoom ratio between the wide-angle state and the telephoto state as expressed by X=0.3* (ft/fw-1) , and Fgd is an absolute value of the amount of movement of the front lens group along the optical axis when zooming from the wide angle end to the telephoto end.
The switching zoom lens as claimed in claim 3, wherein the following condition is satisfied when zooming:

(iii) -2 X -0.1 ≤ Fgd/fw ≤ X +0.1.
The switching zoom lens as claimed in any of the claims 1-4, wherein the most object side lens in the front lens group satisfies the following condition:

(iv) 0.5 ≤ fLo/fw ≤ 1.2,

where fLo is a focal length of the most object side lens of the front lens group.
The switching zoom lens as claimed in claim 5, wherein the following condition is satisfied:

(iv) -2 0.65 ≤ fLo/fw ≤ 1.05.
The switching zoom lens as claimed in any of the claims 1-6, wherein focusing is performed by moving the front lens group along the optical axis at both the wide-angle end and the telephoto end.
The switching zoom lens as claimed in any of the claims 1-7, wherein the most image side lens of the front lens group has a negative refractive power, and the following condition is satisfied:

(v) fLi/fw ≤ -0.5,

where fLi is a focal length of the most image side lens of the front lens group.
The switching zoom lens as claimed in claim 8, wherein the following condition is satisfied:

(v) -2 fLi/fw ≤ -0.7.
A camera module, comprising the switching zoom lens according to any of the claims 1-9, further comprising an image sensor, wherein the image sensor is disposed on the image side of the switching zoom lens, the switching zoom lens is configured to form an optical signal of a photographed object and reflect the optical signal to the image sensor, and the image sensor is configured to convert the optical signal corresponding to the photographed object into an image signal.
A terminal, comprising the camera module according to claim 10 and a Graphic Processing Unit (GPU) , wherein the GPU is connected with the camera module to receive and process the image signal.