Patent Description:
In recent years, with the pursuit of the imaging quality of portable electronic products, dual cameras have become the standard equipment for mobile phone products. In order to achieve high-quality imaging effect, most mobile phones use a solution of "fixed-focus dual-camera", which is a combination of a wide-angle lens and a telephoto lens, therefore the mobile phone can not only perform wide-angle shooting, but also enlarge the scene clearly when shooting in the distance, so that the mobile phone can have a good shooting effect similar to that of signal lens reflex cameras.

In the conventional dual-camera products, the equivalent focal length ratio of the telephoto lens and the wide-angle lens is between <NUM> and <NUM> times, and the zoom ratio can reach <NUM> to <NUM> times when the two are used in combination. The zoom ratio is too small compared with the traditional zoom lens, so it is difficult to meet the requirements of miniaturization and high-definition imaging of portable electronic products.

<CIT> (document D1) discloses an image pick-up lens for a solid-state imaging element including, in order from an object side to an image side, an aperture stop, a first lens of a meniscus shape having a positive refractive power with a convex surface facing the object side, a second lens having a positive refractive power with a concave surface facing the object side, and a third lens having a negative refractive power with a convex surface facing the object side near an optical axis.

<CIT> (document D2) discloses an imaging lens is composed of a first lens with a convex face facing an object side with a positive refraction, an aperture diaphragm, a second lens with a convex face facing an image side with a positive refraction, and a third lens with a concave face facing the image side with a negative refraction.

<CIT> (document D3) discloses a modular zoom contains a telephoto lens and a wide -angle lens, the modular zoom further includes an image processing module or an intelligent image processing system that processes obtained images and realizes zooming characteristics.

The objects of the disclosure are to provide a telephoto lens and a mobile terminal to solve the above problems.

Compared with the related art, the telephoto lens and the mobile terminal provided by the disclosure can achieve a higher zoom ratio. The equivalent focal length of the telephoto lens provided by the disclosure and the conventional wide-angle lens is more than <NUM> times, that is, the telephoto lens provided by the disclosure can achieve zooming of more than <NUM> times when used in combination with the conventional wide-angle lens, thereby better satisfying the requirements of miniaturization and high-definition imaging of electronic products.

The advantages of the invention will be partially given in the following description, and some will become apparent from the following description, or be learned through the practice of the invention.

The following embodiments will further illustrate the invention with reference to the above drawings.

In order to facilitate a better understanding of the invention, the invention will be further explained below with reference to the accompanying drawings. The embodiments of the invention are shown in the drawings, but the invention is not limited to the above-mentioned preferred embodiments. Rather, these embodiments are provided to make the disclosure of the invention more sufficient.

The embodiment of the invention provides a telephoto lens. Form an object side to an imaging surface, the telephoto lens sequentially includes: a first lens having a positive refractive power, a second lens having a refractive power, a third lens having a negative refractive power, a flat glass, and a filter. An object side surface of the first lens is a convex surface, an image side surface of the third lens is a concave surface.

In some embodiments, the telephoto lens meets the expression: <NUM> < TTL/f < <NUM>;
where TTL represents a total optical lens of the telephoto lens, f represents a focal length of the telephoto lens. Satisfying the above expression can effectively shorten the total optical length of the telephoto lens and promote the miniaturization of the telephoto lens.

The flat glass meets the expression: Nd<NUM> > <NUM>;
where Nd<NUM> refers to a refractive index of the flat glass. The flat glass uses a material with high refractive index to facilitate the incidence of the light.

In some embodiments, the first lens is made of glass. Due to the temperature resistance of the glass material is better and the performance is more stable, the first lens is made of glass material, which can effectively achieve the effect of thermalization for the telephoto lens.

In some embodiments, the telephoto lens meets the expression: <NUM> < f/R<NUM> < <NUM>;
where f represents a focal length of the telephoto lens, R<NUM> represents a radius of curvature of the object side surface of the first lens. When the value of f/R<NUM> exceeds the lower limit, the refractive power of the first lens becomes larger, which is not conducive to ensuring the peripheral performance, and the eccentric sensitivity becomes larger. When the value of f/R<NUM> exceeds the upper limit, it is difficult to correct the chromatic aberration of the telephoto lens.

In some embodiments, the telephoto lens meets the expression: <NUM> < R<NUM>/R<NUM> < <NUM>;
where R<NUM> represents a radius of curvature of the object side surface of the first lens, R<NUM> represents a radius of curvature of the image side surface of the third lens. Satisfying the above expression can effectively improve the resolution of the margin field of the telephoto lens.

In some embodiments, the telephoto lens meets the expression: <NUM> < CT<NUM>/CT<NUM> < <NUM>;
where CT<NUM> represents a center thickness of the first lens, CT<NUM> represents a center thickness of the second lens. Satisfying the above expression can effectively shorten the total optical length of the telephoto lens and promote the miniaturization of the telephoto lens.

In some embodiments, the telephoto lens meets the expression: -<NUM> < f<NUM>/f<NUM> < <NUM>;
where f<NUM> represents a focal length of the first lens, f<NUM> represents a focal length of the second lens. When the value of f/R<NUM> exceeds the lower limit, the refractive power and the eccentric sensitivity becomes larger; when the value of f/R<NUM> exceeds the upper limit, the refractive power becomes smaller, which is not conducive to maintaining miniaturization.

In some embodiments, the telephoto lens meets the expression: -<NUM> < f<NUM>/f < <NUM>;
where f<NUM> represents a focal length of the third lens, f represents a focal length of the telephoto lens. When the value of f<NUM>/f exceeds the lower limit, high-order aberration will occur for off-axis lights, and the performance of the telephoto will deteriorate; when the value of f<NUM>/f exceeds the upper limit, it is relatively difficult to correct the field curvature and the coma, and the eccentric sensitivity becomes larger.

In some embodiments, the telephoto lens meets the expression: -<NUM> < (R<NUM> + R<NUM>)/(R<NUM> - R<NUM>) < <NUM>;
where R<NUM> represents a radius of curvature of the object side surface of the second lens, R<NUM> represents a radius of curvature of the image side surface of the second lens. When the value of (R<NUM> + R<NUM>)/(R<NUM> - R<NUM>) exceeds the upper limit, the field curvature and the distortion increase excessively in the positive direction, and are difficult to correct. Conversely, when the value of (R<NUM> + R<NUM>)/(R<NUM> - R<NUM>) exceeds the lower limit, the field curvature and the distortion increase excessively in the negative direction, and also are difficult to correct.

In some embodiments, the telephoto lens meets the expression: -<NUM> < R<NUM>/f<NUM> < <NUM>;
where R<NUM> represents a radius of curvature of the image side surface of the second lens, f<NUM> represents a focal length of the second lens. When the value of R<NUM>/f<NUM> exceeds the lower limit, the refractive power of R<NUM> becomes larger, which is not conducive to ensure the peripheral performance, and the eccentric sensitivity becomes larger; when the value of R<NUM>/f<NUM> exceeds the upper limit, it is difficult to correct the field curvature.

In some embodiments, at least one of the object side surface of the first lens, an image side surface of the first lens, an object side surface of the second lens, an image side surface of the second lens, an object side surface of the third lens, and the image side surface of the third lens is a aspheric surface. A stop is disposed between the object side and the first lens. Aspheric surface can make the telephoto lens have more control variables to reduce aberration.

The embodiment of the invention further provides a mobile terminal. The mobile terminal includes the telephoto lens as mentioned in any above embodiments, the mobile terminal further includes an image sensor, the image sensor is disposed on the imaging surface of the telephoto lens and configured to receive optical signals output by the telephoto lens and form electrical signals corresponding to the optical signals.

The shapes of aspheric surfaces of the optical lens provided by the embodiments of the invention satisfy the following equation: <MAT> where z represents a vector height between a position on the surface and a vertex of the surface along an optical axis of the lens, c represents a curvature of the vertex of the surface, K is a quadratic surface coefficient, h is a distance between the position on the surface and the optical axis, B is a fourth order surface coefficient, C is a sixth order surface coefficient, D is an eighth order surface coefficient, E is a tenth order surface coefficient, F is a twelfth order surface coefficient, G is a fourteenth order surface coefficient, H is a sixteenth order surface coefficient.

Compared with a conventional telephoto lens, the telephoto lens provided by the invention can achieve a higher zoom ratio. The zoom ratio refers to the ratio of the equivalent focal length of the telephoto lens to the equivalent focal length of the wide-angle lens under the premise of the same pixels. Equivalent focal length = actual focal length * focal length conversion factor; focal length conversion factor = <NUM> / the diagonal length of the target surface of the image sensor.

The equivalent focal length of the telephoto lens provided by the disclosure and the conventional wide-angle lens is more than <NUM> times, that is, the telephoto lens provided by the disclosure can achieve zooming of more than <NUM> times when used in combination with the conventional wide-angle lens, thereby better satisfying the requirements of miniaturization and high-definition imaging of electronic products.

The invention will be further described in the following multiple embodiments. In each of the following embodiments, the thickness and radius of curvature of each lens in the telephoto lens are different. For specific differences, refer to the parameter table in each embodiment.

Please refer to <FIG>, which is a structural diagram of a telephoto lens <NUM> provided in a first embodiment of the disclosure. From an object side to an imaging surface thereof, the telephoto lens <NUM> sequentially includes a stop ST, a first lens L1, a second lens L2, a third lens L3, a flat glass G1 and a filter G2.

The first lens L1 has a positive refractive power, an object side surface S1 of the first lens L1 is a convex surface and an image side surface S2 of the first lens L1 is a concave surface. The first lens is made of glass, and the object side surface S1 of the first lens L1 and the image side surface S2 of the first lens L1 are both aspheric surfaces. The second lens L2 has a positive refractive power, an object side surface S3 of the second lens L2 is a convex surface, an image side surface S4 of the second lens L2 is a concave surface. The third lens L3 has a negative refractive power, an object side surface S5 of the third lens L3 is a convex surface, an image side surface S6 of the third lens L3 is a concave surface.

Related parameters of each lens in the telephoto lens <NUM> provided by the first lens are shown in Table <NUM>.

The parameters of the aspheric surfaces of the first lens of this embodiment are shown in Table <NUM>.

<FIG> shows field curvature curves of the telephoto lens <NUM> in this embodiment, <FIG> shows axial spherical aberration curves of the telephoto lens <NUM> in this embodiment, <FIG> shows lateral chromatic aberration curves of the telephoto lens <NUM> in this embodiment. As can be seen from the figures, the field curvature, the axial spherical aberration, the lateral chromatic aberration and the distortion of the telephoto lens <NUM> of this embodiment are all corrected well.

Please refer to <FIG>, which is a structural diagram of a telephoto lens <NUM> provided in this embodiment. The telephoto lens <NUM> in this embodiment is substantially similar to the telephoto lens <NUM> in the first embodiment expect that: a second lens L2 of the telephoto lens <NUM> has a negative refractive power, an object side surface S3 of the second lens L2 and an image side surface S4 of the second lens L2 are both aspheric surface, and the radius of curvature and the materials of each lens are different. Related parameters of each lens are shown in Table <NUM>.

The parameters of the aspheric surfaces of the lenses of this embodiment are shown in Table <NUM>.

<FIG> shows field curvature curves of the telephoto lens <NUM> in this embodiment, <FIG> shows axial spherical aberration of the telephoto lens <NUM> in this embodiment, <FIG> shows lateral chromatic aberration curves of the telephoto lens <NUM> in this embodiment. As can be seen from the figures, the field curvature, the axial spherical aberration, the lateral chromatic aberration, and the distortion of the telephoto lens <NUM> of this embodiment are all corrected well.

Please refer to <FIG>, which is a structural diagram of a telephoto lens <NUM> provided in this embodiment. The telephoto lens <NUM> in this embodiment is substantially similar to the telephoto lens <NUM> in the first embodiment expect that: a first lens L1 and a second lens L2 of the telephoto lens <NUM> form a cemented lens, the second lens L2 has a negative refractive power, and the radius of curvature and the materials of each lens are different. Related parameters of each lens are shown in Table <NUM>.

<FIG> shows field curvature curves of the telephoto lens <NUM> in this embodiment, <FIG> shows axial spherical aberration of the telephoto lens <NUM> in this embodiment, <FIG> shows lateral chromatic aberration curves of the lateral chromatic aberration of the telephoto lens <NUM> in this embodiment. As can be seen from the figures, the field curvature, the axial spherical aberration, the lateral chromatic aberration and the distortion of the telephoto lens <NUM> of this embodiment are all corrected well.

Please refer to <FIG>, which is a structural diagram of a telephoto lens <NUM> provided in this embodiment. The telephoto lens <NUM> in this embodiment is substantially similar to the telephoto lens <NUM> in the first embodiment expect that: an image side surface of a second lens L2 of the telephoto lens <NUM> is a convex surface, and the radius of curvature and the materials of each lens are different. Related parameters of each lens are shown in Table <NUM>.

<FIG> shows field curvature curves of the telephoto lens <NUM> in this embodiment, <FIG> shows axial spherical aberration of the telephoto lens <NUM> in this embodiment, <FIG> shows lateral chromatic aberration curves of the telephoto lens <NUM> in this embodiment. As can be seen from the figures, the field curvature, the axial spherical aberration, the lateral chromatic aberration and the distortion of the telephoto lens <NUM> of this embodiment are all corrected well.

Table <NUM> shows the optical characteristics corresponding to the telephoto lens in the above four embodiments, including the total optical length TTL, the focal length f, the aperture number F #, and the field angle 2θ, and the value corresponding to each of the above conditional expression.

The total optical length of the telephoto lens provided by the disclosure exceeds <NUM>, which is far more than the thickness of a mobile phone. When the telephoto lens is used in a mobile phone, the lens can be designed as a periscope lens imaging system using a reflective optical surface, which is embedded in the mobile phone to the meet the requirements of thin and light electronics product.

The focal lens of the telephoto lens provided by the disclosure reach <NUM>, and the diagonal length of the image sensor matched with the telephoto lens is <NUM>, and the calculation method of the equivalent focal length can be obtained: (<NUM>) focal length conversion factor = <NUM> / the diagonal length of the target surface of the image sensor = <NUM> / <NUM> = <NUM>; (<NUM>) equivalent focal length = actual focal length * focal length conversion factor = <NUM> * <NUM> = <NUM>. Therefore, the equivalent focal length of the telephoto lens provided by the disclosure can reach <NUM>. Generally, the equivalent focal length of a conventional wide-angle lens is usually <NUM> ~<NUM>. When the telephoto lens provided by the disclosure is used in combination with a conventional wide-angle lens, the equivalent focal length ratio of the two is more than <NUM> times, that is, the telephoto lens provided by the disclosure can achieve zooming of more than <NUM> times when used in combination with the conventional wide-angle lens, thereby having better zoom imaging effects and better satisfying the requirements of miniaturization and high-definition imaging of electronic products.

Please refer to <FIG>, the embodiment provides a mobile terminal <NUM> including an image sensor <NUM> and a telephoto lens in any of the foregoing embodiments, such as the telephoto lens <NUM>. The image sensor <NUM> is disposed on the imaging surface S11 of the telephoto lens <NUM>, and configured to receive optical signals output by the telephoto lens and form electrical signals corresponding to the optical signals.

The image sensor <NUM> may be a Complementary Metal Oxide Semiconductor (CMOS) image sensor, or a Charge Coupled Device (CCD) image sensor.

The total optical length TTL of the telephoto lens provided by the disclosure can reach <NUM>, which is far more than the thickness of the mobile terminal <NUM>. When the telephoto lens <NUM> is disposed in the mobile terminal <NUM>, the mobile terminal <NUM> further includes a first prism <NUM> and a second prism <NUM>. The first prism <NUM> is disposed at an entrance of the telephoto lens, and the second prism <NUM> is disposed at an exit of the telephoto lens <NUM>, thereby designing the telephoto lens <NUM> as a periscope lens imaging system (the incident light and the exit light are perpendicular to different planes) using reflective optical surfaces of the prisms, shortening a transmission distance of the optical path, and meeting the miniaturization requirements of the mobile terminal <NUM>.

As shown in the perspective of <FIG>, the first prism <NUM> turns the incident light (incident parallel to the paper surface) into the telephoto lens <NUM>, and the second prism <NUM> turns the light emitted by the telephoto lens <NUM> again to form the exit light (exit perpendicular to the paper surface), the incident light and the exit light form a vertical relationship.

The mobile terminal <NUM> provided by the embodiment includes the telephoto lens <NUM>, which can achieve a higher zoom ratio than a conventional telephoto lens, and can better satisfy the requirements of miniaturization and high-definition imaging of electronic products.

Claim 1:
A telephoto lens (<NUM>), from an object side to an imaging surface thereof, sequentially comprising a stop surface (ST);
a first lens (L1) having a positive refractive power, an object side surface (S1) of the first lens (L1) being convex;
a second lens (L2) having a refractive power;
a third lens (L3) having a negative refractive power, an image side surface (S6) of the third lens (L3) being concave;
a flat glass (G1); and
a filter (G2); characterized in that an object side surface (S3) of the second lens (L2) is convex;
the flat glass (G1) meets the expression: Nd4 > <NUM>, where Nd4 represents a refractive index of the flat glass (G1), and a focal length of the telephoto lens (<NUM>) is capable of reaching <NUM>.