TW201839453A - Fixed focus lens - Google Patents

Abstract

A fixed focus lens comprising two lens groups separated by an aperture, the lens group close to the magnifying end comprising three lenses, the lens group close to the minifying end having four lenses. While in focusing process, the interval between the first lens group, the aperture and the second lens group is fixed and moves relative to the light valve along the optical axis as a whole. The first lens group and the second lens group has an aspherical lens respectively. The ratio of the back focal length (BFL equivalent in air) to the effective focal length of the fixed focus lens is greater than or equal to 1.3.

Description

Fixed focus lens

The present invention relates to an optical lens, and more particularly to a fixed focus lens.

With the advancement of photoelectric technology, imaging devices such as projectors, digital cameras and digital cameras have been widely used in daily life. One of the core components of these imaging devices is an optical lens. By adjusting the optical lens, the image is clearly focused on the screen or the charge-coupled element for imaging. Therefore, the imaging quality is closely related to the optical quality of the optical lens. In a highly competitive market, manufacturers are committed to improving the optical quality of fixed-focus lenses, and reducing their weight, volume, and production costs to enhance the competitive advantages of the aforementioned imaging devices. Therefore, how to make a fixed-focus lens that is miniaturized and high-performance and has the characteristics of low aberration, large aperture, cheapness, and high resolution is one of the important topics for those skilled in the art.

Other objects and advantages of the present invention can be further understood from the technical features disclosed in the embodiments of the present invention.

According to an aspect of the present invention, a fixed-focus lens is proposed, which includes a first lens group, an aperture, and a second lens group in order from the magnification side to the reduction side. The first lens group includes a first lens, a second lens, and a third lens in order, and the first lens group includes at least one aspheric lens; the second lens group includes a fourth lens, a fifth lens, A sixth lens and a seventh lens, and the second lens group includes a cemented lens and an aspheric lens; furthermore, BFL is the back focal length of the fixed focus lens, EFL is the effective focal length of the fixed focus lens, and the fixed focus lens conforms to The condition of BFL / EFL ≧ 1.3.

If a glass lens is used for the first piece of the fixed-focus lens of the embodiment, it solves the problems of being easily scratched, manufacturability, and high cost when using an aspherical lens. In addition, if two lenses with opposite diopters are arranged in the front and rear groups, the problem of thermal drift and focus easily generated by the lens in a high-temperature use environment is also solved. Furthermore, the use of cemented lenses can reduce the residual lateral chromatic aberration in the system. Therefore, it is possible to provide a fixed focus lens design with good aberration capability, easy miniaturization, and better imaging quality.

In order to make the above features and advantages of the present invention more comprehensible, embodiments are hereinafter described in detail with reference to the accompanying drawings.

The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of various embodiments with reference to the drawings. The directional terms mentioned in the following embodiments, such as "up", "down", "front", "rear", "left", "right", etc., are only directions referring to the attached drawings. Therefore, the directional terms used are used for illustration, not for limiting the present invention. In addition, the terms "first" and "second" used in the following examples are used to identify the same or similar elements, and are not intended to limit the elements. In addition, the following embodiments are only further described for the projection device and the display system. Those skilled in the art can apply this connection system to any required situation according to actual needs. The so-called lens in the present invention means that at least part of the light can be penetrated, and the radius of curvature of at least one of its light-in and light-out surfaces is not infinite; in other words, at least one of the light-in and light-out surfaces of the lens Those need to be non-planar. For example, flat glass is not a lens according to the present invention. In addition, the so-called zoom side of the present invention is the side closer to the projection surface (such as a projection screen) when the designated focus lens is used in a projection system; the zoom side is closer to the light valve when the designated focus lens is used in the projection system. The side. When a fixed-focus lens is used in an image capturing system, the zoom side refers to the side closer to the subject, and the zoom side refers to the side closer to the photosensitive element.

An embodiment of the present invention provides a fixed focus lens. With the design of the embodiment of the present invention, it is possible to provide a fixed focus lens design with good aberration capability, easy miniaturization, and better imaging quality.

FIG. 1 is a schematic diagram of a fixed focus lens according to an embodiment of the present invention. Referring to FIG. 1, in this embodiment, the fixed-focus lens 1 has a lens barrel (not shown), and the lens barrel contains components such as a first lens group 10, an aperture 20, and a second lens group 30. The diaphragm 20 is provided between the first lens group 10 and the second lens group 30. That is, with the aperture 20 as the dividing line, the fixed-focus lens 1 may include first and second lens groups 10 and 30, and a side of the second lens group 30 opposite to the reduction side may further be equipped with a penetration smooth Image devices TSP (Transmissive Smooth Picture), 稜鏡 PR, glass cover CG, and light valve LV. In this example, the entire first lens group 10, the aperture 20, and the second lens group 30 can be focused by moving back and forth along the optical axis A relative to the imaging plane. That is, when focusing, the interval (Interval) between the first lens group 10, the aperture 20, and the second lens group 30 of the fixed focus lens 1 is fixed. In this example, the imaging plane and the surface of the light valve LV are coplanar. The light valve LV in the present invention refers to an optical device capable of converting illumination light into image light, such as DMD, LCD, LCOS, etc., which is known to those skilled in the art. In this example, the light valve is a DMD. In addition, in this example, in addition to being a telecentric lens, the fixed-focus lens 1 is also an inverted telenes. For example, when the lens has two parts, when the sum of the diopters of the parts closer to the magnification side (such as lenses L1 and L2) is negative, the corresponding diopter of the other parts (such as lenses L3 to L8) When the sum is positive, the lens is a reverse telescope lens.

In this example, the first lens group 10 has a positive refractive power, and the second lens group 30 has a positive refractive power. The first lens group 10 includes a lens L1, a lens L2, and a lens L3 which are sequentially arranged along the optical axis A from the magnification side (left side in FIG. 1) to the reduction side (right side in FIG. 1). The second lens group 30 includes a lens L4, a lens L5, a lens L6, a lens L7, and a lens L8, which are sequentially arranged along the optical axis from the magnification side to the reduction side. The diopters L1-L8 are negative, negative, and positive; positive, negative, positive, negative, and positive. In addition, the sum of the diopters of the lenses L1 and L2 is negative, and the sum of the diopters of the lenses L1, L2, and L3 is positive; and the sum of the diopters of the lenses L4 to L8 is positive. The lenses L1-L8 are made of glass, plastic, glass; plastic, glass, glass, glass, and glass. In addition, if S is a spherical lens and ASP is an aspherical lens, the lenses L1-L8 are S, ASP, S, ASP, S, S, S, and S, respectively. In addition, the optical surface shapes of the lenses L1-L8 are convexoconcave, convexoconcave, convexoconvex; convexoconcave, concaveconvex, convexoconvex, convexoconcave, and convexoplanar.

The design parameters of the lens and its peripheral components of the fixed focus lens 1 are shown in Table 1. However, the materials listed below are not intended to limit the present invention. Any person with ordinary knowledge in the field can refer to the present invention to make appropriate changes to its parameters or settings, but it should still fall within the scope of the present invention. .

Table I

In addition, * in the table means that the surface is an aspherical surface, and if it is not marked, it means a spherical surface. In the following design examples of the present invention, the aspheric polynomial is expressed by the following formula:

In the above formula, x is the offset (sag) in the direction of the optical axis A, c ′ is the inverse of the radius of the osculating sphere, that is, the inverse of the radius of curvature near the optical axis A, and k is the conic coefficient (conic constant), y is the aspheric height, that is, the height from the lens center to the lens edge. A-G represents the aspheric coefficients of each order of the aspheric polynomial. Table 2 lists the values of aspheric coefficients and quadric surface coefficients of each order on the surface of each lens in the lens in the first specific embodiment of the present invention.

Table II

According to the design of the above embodiment, in order to solve the problems of aspherical lens, easy to be scratched, manufacturability and high cost, in this example, the first lens of the front group (magnification side) and the rear group (reduction side) are last One lens uses a glass spherical lens, and the lens L2 and the lens L4 are designed as aspheric lenses, and the lenses L2 and L4 are respectively disposed on both sides of the aperture, rather than on the same side.

In addition, in order to solve the lens shifting that is likely to occur in a high-temperature use environment, the lens L2 and the lens L4 of the previous example are designed to have positive and negative refractive powers, and the amount of focus shift in the system must be offset and slowed down. In addition, the first and last lenses of the previous example use spherical lenses, and there will be more lateral color aberrations in the system. Therefore, lenses L5, L6, and L7 are arranged as triple cemented lenses to reduce the remaining lenses in the system. Lateral chromatic aberration. That is, the lenses L5, L6, and L7 include two lenses cemented to each other. It should be noted that, in this example, the triple cemented lens is disposed between the aperture and the reduction side. The so-called lens cementation or cementation lens in the present invention refers to a lens group in which a plurality of lenses are fixed to each other and fixed, but the fixing means is not limited to the glue. For example, in this example, the three lenses are fixed by optical colloids, but it is not limited to this. When needed, the three lenses can also be used, for example, by mechanical means (such as positioning grooves). Clamp and fix it.

In addition, the EFL referred to in the present invention refers to an effective focal length of the system. TTL refers to the total track length (Total Track Length), that is, from the first surface of the first lens L1 on the magnification side of the fixed focus lens, measured along the optical axis of the lens to the reduction side, and measured to imaging The distance of the plane. In this embodiment, the surface S22 and the imaging plane of the fixed focus lens 1 are coplanar. The so-called back focal length or BFL in the present invention refers to the back focal length equivalent in air of a given focal lens. For example, the back focal length BFL is all components outside the lenses L1 to L8. When replaced with air, the equivalent back focal length of the lenses L1 to L8 is measured. In this example, the second lens group 30 is provided with a TSP toward the reduction side, so its BFL is larger than that of a general lens. For example, the BFL can be between 9 and 20 mm, and preferably between about 10 and 16. On the other hand, usually BFL / EFL will be between 1 and 5, such as greater than 1.3, or between 1.3 and 2.

In this example, the aperture value of the fixed focus lens 1 is about 1.6; the EFL is about 8.842mm; the TTL is about 87.977mm; and the BFL is about 13.11mm. The BFL / EFL is about 1.4826. The small EFL and small TTL characteristics of fixed-focus lenses allow the aforementioned fixed-focus lenses to be used in portable projectors that include batteries and do not require external power supply.

In addition, it is worth mentioning that, in another embodiment, in addition to the aforementioned lenses in the lens 1, the transmissive smooth image device TSP indicated on the surfaces S16 and S17, for example, may be selectively used; Any one of the 稜鏡 PR marked on S18 and S19; the glass protective cover marked on the surfaces S20 and S21 and the light valve LV on the surface S22 are placed inside the lens barrel.

The design of the second specific embodiment of the fixed focus lens of the present invention will be described below. Considering that its design is similar to that of the first specific embodiment, only the differences will be explained separately, and the rest will not be repeated because they correspond to the first specific embodiment.

In this example, the design parameters of the lens and its peripheral components in the fixed focus lens 1 are shown in Table 3.

Table three

Table 4 lists values of aspheric coefficients and quadric surface coefficients of each order on the surface of each lens of the lens in the second embodiment of the present invention.

Table four

As can be seen from Tables 3 and 4, one of the main differences between the second embodiment and the first embodiment is that both surfaces S14 and S15 of the last lens of the fixed-focus lens 1 near the reduction side are aspherical surfaces. In addition, in this example, the BFL / EFL is about 1.4828.

The design of the third specific embodiment of the fixed focus lens of the present invention will be described below. Considering that its design is similar to that of the first specific embodiment, only the differences will be explained separately, and the rest will not be repeated because they correspond to the first specific embodiment.

In this example, the design parameters of each lens and its peripheral components in the fixed focus lens 1 are shown in Table 5.

Table five

Table 6 lists values of aspheric coefficients and quadric surface coefficients of each order on the surface of each lens of the lens in the third embodiment of the present invention.

Table six

As can be seen from the above table, the main difference between the third embodiment and the first embodiment is that both surfaces of the last lens of the fixed-focus lens 1 near the reduction side are aspherical surfaces. In addition, in this example, the rear group includes two sets of double cemented lenses. In this example, the BFL / EFL is about 1.451.

Furthermore, in another embodiment of the present invention, a projector is disclosed. In addition to the fixed-focus lens 1 in each of the embodiments, it also includes the aforementioned light valve and illumination light source, which can be used for An image is imaged on a projection surface such as a projection screen.

Furthermore, in another embodiment of the present invention, an image capturing device such as a camera is disclosed. In addition to the fixed-focus lens 1 in each of the embodiments, a photographic element is further included for capturing. The image light of an object.

It can be known from the above embodiments that the first lens of the fixed-focus lens uses a glass lens, which solves the problems of easy scratching, manufacturability, and high cost when using an aspherical lens. In addition, by setting two lenses with opposite diopters in the front and rear groups, the problem of lens shifting that easily occurs in a high-temperature use environment is also solved. Furthermore, the use of cemented lenses can reduce the residual lateral chromatic aberration in the system. Therefore, it is possible to provide a fixed focus lens design with good aberration capability, easy miniaturization, and better imaging quality.

The parameters listed in Tables 1 to 6 are for illustration only and do not limit the present invention. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and retouching without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection shall be determined by the scope of the attached patent application. In addition, any embodiment of the present invention or the scope of patent application does not need to achieve all the purposes or advantages or features disclosed by the invention. In addition, the abstract and the title are only used to assist the search of patent documents, and are not intended to limit the scope of rights of the present invention.

1‧‧‧ fixed focus lens

10‧‧‧The first lens group

20‧‧‧ aperture

30‧‧‧Second lens group

TSP‧‧‧ Penetrating Smooth Image Device

PR‧‧‧ 稜鏡

CG‧‧‧glass protective cover

LV‧‧‧Light Valve

L1 ~ L8‧‧‧ lens

A‧‧‧ Optical axis

FIG. 1 is a schematic diagram of a fixed focus lens according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a fixed focus lens according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram of a fixed focus lens according to a third embodiment of the present invention.

no

Claims (11)

A fixed-focus lens includes, from a magnification side to a reduction side, a first lens group, an aperture, and a second lens group in order; wherein the first lens group includes a first lens, a second lens, and And a third lens, and the first lens group includes at least one aspheric lens; the second lens group includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens, and the first lens group The two lens groups include a cemented lens and an aspherical lens; moreover, BFL is the back focal length of the fixed focus lens, EFL is the effective focal length of the fixed focus lens, and the fixed focus lens meets the conditions of BFL / EFL ≧ 1.3. A fixed focus lens, in order from the magnification side to the reduction side, includes: a first lens; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; and a seventh One of the first lens, the second lens, and the third lens is an aspheric lens; one of the fourth lens, the fifth lens, the sixth lens, and the seventh lens The lens is an aspheric lens; two lenses of the fourth lens, the fifth lens, the sixth lens, and the seventh lens are cemented with each other; BFL is the back focal length of the fixed focus lens, and BFL of the fixed focus lens ≧ 11, TTL is the total optical path length of the fixed focus lens, and TTL ≦ 150mm. The fixed-focus lens according to any one of claim 1 or 2, wherein the first lens, the second lens, and the third lens include at least one glass spherical lens; the fourth lens, The fifth lens, the sixth lens and the seventh lens at least include a glass spherical lens. The fixed-focus lens according to any one of claim 1 or 2, wherein the refractive power of the aspheric lens of the first lens, the second lens, and the third lens is the same as that of the fourth lens The refractive power of the aspheric lens of the fifth lens, the sixth lens, and the seventh lens is opposite. The fixed-focus lens according to any one of the first or second item of the claim, wherein EFL is the effective focal length of the fixed-focus lens and BFL / EFL ≧ 1.45. The fixed-focus lens according to any one of claim 1 or 2, wherein the sum of the refractive powers of the first lens and the second lens is negative, and the refractive power of the third lens is positive The fixed-focus lens according to any one of claim 1 or 2, wherein the sum of the diopters of the first lens, the second lens, and the third lens is positive. The fixed-focus lens according to any one of claim 1 or 2, further comprising an eighth lens disposed between the third lens and the reduction side. The fixed-focus lens according to claim 8, wherein three lenses of the fourth lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are cemented into one triple cement lens. The fixed-focus lens according to item 2 of the claim, further comprising an aperture disposed between the third lens and the fourth lens. The fixed-focus lens according to claim 1 or 2, wherein the order from the magnification side to the reduction side includes: the first lens is negative diopter; the second lens is negative diopter The third lens is positive diopter; the fourth lens is positive diopter; the fifth lens is negative diopter; the sixth lens is positive diopter; an eighth lens is negative diopter; and the seventh lens is negative The lens has a positive dioptric power; wherein the fifth lens, the sixth lens, and the eighth lens form a triple cemented lens with negative diopter, the first lens, the second lens, and the third lens have a refractive power of The sum is positive, TTL is the total optical path length of the prime lens, TTL ≦ 150mm, BFL is the back focal length of the prime lens, BFL ≧ 11 of the prime lens, and EFL is the effective focal length of the prime lens, The fixed-focus lens meets the condition of BFL / EFL ≧ 1.3, the number of lenses of the fixed-focus lens is less than 10, the aperture value of the fixed-focus lens is less than 2, and the field of view (FOV) of the fixed-focus lens is less than 100 degrees.