Prime lens

Abstract

The utility model discloses a prime lens which comprises three lens groups. The first lens group with the positive focal power comprises a meniscus positive lens, a pair of doublet lenses with a cemented surface approximate to a plane and another meniscus positive lens, and the distance between the central axes of the last two lenses is less than 1.0 mm. The movable second lens group is only provided with one negative lens, and the absolute value of the focal length is 0.7 time of the total focal length of the prime lens. And the third lens group with the positive focal power comprises a pair of doublet lenses, a biconvex spherical positive lens, a biconcave spherical negative lens, another pair of doublet lenses and a meniscus negative lens. The prime lens can be used for a full-frame camera, does not contain an aspheric surface, and is low in cost.

Description

Technical Field

[0001] This utility model belongs to the field of photographic lens technology, specifically relating to a fixed-focus lens that can be used in full-frame cameras. Background Technology

[0002] Mirrorless cameras (SLT cameras) are currently popular non-professional digital cameras, equipped with full-frame or APS-C sensors and interchangeable lenses. High-quality lenses are expensive, and autofocus consumes a lot of power.

[0003] Patent CN108474925A discloses an imaging lens with only one aspherical surface. When focusing, it moves two cemented doublet lenses or 2-3 lenses in the middle, with a total focal length of about 80mm and a maximum aperture of F / 1.45. Utility Model Content

[0004] The technical problem to be solved by this invention is how to improve a fixed-focus lens to adapt it to a mirrorless camera.

[0005] This utility model discloses a fixed-focus lens.

[0006] This fixed-focus lens can be used in full-frame cameras. It includes a first lens group with positive optical power, a second lens group with negative optical power, and a third lens group with positive optical power, which are distributed sequentially along the central axis. It also includes an aperture stop. When focusing from infinity to a close object, the first lens group, the aperture stop, and the third lens group are fixed relative to the image plane, while the second lens group moves along the central axis to the image plane.

[0007] The first lens group comprises the following elements distributed sequentially along the central axis:

[0008] The first lens is configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side;

[0009] The second lens is configured as a biconvex spherical positive lens with an image-side radius of curvature of -750 ~ -800 mm and an Abbe number greater than 80.0.

[0010] The third lens is configured as a biconcave spherical negative lens, cemented together with the second lens, with an Abbe number of 23.0~28.0; and

[0011] The fourth lens is configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side. Its distance from the central axis of the third lens is no greater than 1.0 mm, and its Abbe number is greater than 80.0.

[0012] The second lens group includes only the fifth lens, which is a biconcave spherical negative lens with an absolute focal length of 0.7 times the total focal length of the fixed-focus lens.

[0013] The third lens group includes the following elements distributed sequentially along the central axis:

[0014] The sixth lens is configured as a negative lens, with a convex spherical surface on the object side and a concave spherical surface on the image side;

[0015] The seventh lens is configured as a positive lens and is cemented together with the sixth lens; its image-side surface is a concave spherical surface.

[0016] The eighth lens is configured as a biconvex spherical positive lens;

[0017] The ninth lens is configured as a biconcave spherical negative lens, with a central axis distance of 0.15 mm from the eighth lens, and an Abbe number of 23.0~28.0;

[0018] The tenth lens is configured as a biconvex spherical positive lens with an Abbe number of 23.0~28.0;

[0019] The eleventh lens, configured as a biconcave spherical negative lens, is cemented to the tenth lens and has an Abbe number greater than 80.0; and

[0020] The twelfth lens is configured as a negative lens, with a concave spherical surface on the object side and a convex spherical surface on the image side.

[0021] In some embodiments of this application, the total focal length of the fixed-focus lens may be selected to be 75-85 mm. Further, the second lens, the fourth lens, and the eleventh lens have the same Abbe number and refractive index; the third lens, the ninth lens, and the tenth lens have the same Abbe number and refractive index.

[0022] The following beneficial effects can be obtained by implementing the technical solution of this utility model.

[0023] This utility model discloses a fixed-focus lens comprising three lens groups. The first lens group, with positive optical power, includes a meniscus positive lens, a cemented doublet with an approximately flat cemented surface, and another meniscus positive lens; the central axis distance between the last two lenses is less than 1.0 mm. The movable second lens group contains only one negative lens with an absolute focal length of 0.7 times the total focal length of the fixed-focus lens. The third lens group, with positive optical power, includes a cemented doublet lens, a biconvex spherical positive lens, a biconcave spherical negative lens, another cemented doublet lens, and a meniscus negative lens. This fixed-focus lens can be used in full-frame cameras, is low-cost due to the absence of aspherical elements. Attached Figure Description

[0024] The accompanying figures should be used in conjunction with the detailed implementation section.

[0025] Figure 1 This is a cross-sectional view of the central axis of the fixed-focus lens in Embodiment 1. The captions represent: IMG - image plane, FIT - filter protector, STO - aperture stop, Z1 - central axis, T1 - movement range, and REF - reference starting plane.

[0026] Figure 2 This is the optical path diagram of the fixed-focus lens when it focuses on infinity in Example 1;

[0027] Figure 3a and Figure 3b In Example 1, the spherical aberration map and transverse chromatic aberration map of the fixed-focus lens were calculated by ZEMAX software. The calculation conditions were: incident light mixing range 425~658nm, incident pupil radius 22.7618mm, aperture F / 1.8, and infinity focus state.

[0028] Figure 4a and Figure 4b The graphs shown are two modulation transfer function (MTF) curves of a fixed-focus lens calculated by ZEMAX software in Example 1, with the calculation conditions as described above. Detailed Implementation

[0029] The embodiments are described below with reference to the accompanying drawings.

[0030] In this specification, unless otherwise specified, one embodiment, some embodiments and other embodiments are used to distinguish different embodiments and do not refer to all embodiments in general; the directions / positions indicated by top, bottom, center, edge, inner, outer, far, near, long, wide, vertical, horizontal, up, down, front, back, left, right, etc. are based on the observation angle of the accompanying drawings and should not be understood as the component / device being located in a specific position or facing a specific direction.

[0031] The lens grouping method described in this specification is for the convenience of illustrating the embodiments only. It is understood that other grouping methods may be used in optical design analysis, lens forming, and lens assembly.

[0032] Positive lens and positive optical power both refer to an optical system with a positive image-side focal length, which converges parallel incident light beams. Negative lens and negative optical power both refer to an optical system with a negative image-side focal length, which diverges parallel incident light beams. The light-transmitting surface of a lens can be simply referred to as the "surface." The side of the lens facing the subject is called the "object-side surface," and the side of the lens facing the camera's image sensor is called the "image-side surface."

[0033] The aperture stop, also known as the "stop," is numbered along with the lens's light-transmitting surface.

[0034] Example 1

[0035] A fixed-focus lens is disclosed.

[0036] This fixed-focus lens has a focal length of 85mm, a maximum aperture of F / 1.8, and can be used with full-frame cameras.

[0037] Please see Figure 1 and Figure 2 . Figure 1The lens tube is not shown in the figure. The central axis Z1 (also known as the optical axis, principal axis, or principal optical axis) points from left to right to the image plane IMG. A filter protector FIT is located in front of the image plane IMG.

[0038] Table 1 below lists the data and positional relationships of each lens in this fixed-focus lens.

[0039]

[0040] In Table 1, the object-side surface of the first lens L1 is denoted as surface S1. Other light-transmitting surfaces (including the plane containing the aperture stop STO and the cemented surface) are numbered in ascending order along the central axis Z1. The image-side surface of the twelfth lens L12 is denoted as surface S22. "Radius of curvature R" represents the paraxial radius of curvature at the vertex of a surface. The i-th surface S... i and the (i+1)th surface S i+1 For lenses between two adjacent lenses: their "thickness" is the central axis thickness, and their "refractive index Nd" and "Abbe number Nd" are measured values ​​on the d-line. The distance between the image-side surface of the first lens and the object-side surface of the second lens on the central axis Z1 is called the central axis distance between them.

[0041] This fixed-focus lens has 12 elements, all of which are spherical glass lenses, numbered sequentially along the central axis and divided into three groups. The lens barrel of this fixed-focus lens ( Figure 1 (Not shown) Along the central axis Z1, from the object side to the image side, the first lens group G1, the second lens group G2, the aperture stop STO, and the third lens group G3 are arranged sequentially. The reference starting plane REF is located at the vertex section of the first lens L1, approximately 104 mm away from the central axis of the image plane IMG. Because aspherical lenses are not used, the length of this fixed-focus lens exceeds 100 mm.

[0042] During the focusing process of this fixed-focus lens, only the second lens group G2 can be moved back and forth along the central axis Z1 by a stepper motor. The first lens group G1, the aperture stop STO, and the third lens group G3 are all fixed in position relative to the image plane IMG. The distance between the central axis of the aperture stop STO and the surface S11 of the third lens group G1 is approximately 1.5 mm, and the distance between the central axis of the image plane IMG and the surface S22 of the third lens group G3 is approximately 16.0 mm.

[0043] The first lens group G1 has positive optical power and consists of four glass lenses: a meniscus positive lens, a cemented doublet with a nearly flat cemented surface, and another meniscus positive lens. These four glass lenses are arranged sequentially along the central axis Z1 as lens L1, lens L2, lens L3, and lens L4. Of all 12 lenses, lens L1 has the largest aperture. In the cemented doublet formed by lens L2 and lens L3, the object-side surface is convex spherical, the image-side surface is concave spherical, and the cemented surface is nearly flat but has a negative radius of curvature. The central axis distance between lens L4 and lens L3 is less than 1.0 mm.

[0044] The second lens group G2 can move along the central axis during focusing. The second lens group G2 consists of only a fifth lens L5 made of a single piece of glass. The fifth lens L5 is a biconcave spherical negative lens with a focal length of -60mm, and its absolute value is 0.7 times the total focal length of the fixed-focus lens.

[0045] The third lens group G3 has positive optical power and consists of seven glass lenses, including, in sequence, a cemented doublet, a biconvex spherical positive lens, a biconcave spherical negative lens, another cemented doublet, and a meniscus negative lens. These six glass lenses are arranged along the central axis Z1 as follows: lens L6, lens L7, lens L8, lens L9, lens L10, lens L11, and lens L12. Lens L6 is a meniscus negative lens, and lens L7 is a meniscus positive lens. In the cemented doublet formed by these two lenses, the object-side surface is convex spherical, and the image-side surface is concave spherical and approximately planar, with a positive radius of curvature at the cemented surface. In the other cemented doublet formed by cementing lens L10 and lens L11, the object-side surface is convex spherical, and the image-side surface is concave spherical, with a negative radius of curvature at the cemented surface. The radii of curvature on both sides of lens L12 are negative.

[0046] All 12 glass lenses are arranged sequentially along the central axis Z1 to form the three lens groups mentioned above, and are installed inside the lens barrel. The lens barrel is equipped with a stepper motor and a power input interface.

[0047] Figure 1 The second lens group G2 (i.e., the fifth lens L5) is located at the object-side boundary of its movement range T1, approximately 2.4 mm from the central axis of the fourth lens L4 and approximately 13.0 mm from the central axis of the aperture stop STO. At this time, the fixed-focus lens is in focus at infinity; please refer to Figure 3 for the optical path diagram. When focusing on a close-up object, the second lens group G2 moves along its central axis to the image plane IMG, without exceeding the image-side boundary of its movement range T1. Because only a single lens element moves, the focusing electrical load of this fixed-focus lens is low, reducing camera power consumption.

[0048] The specific focal lengths of each glass lens, each cemented doublet lens, and each of the three lens groups in this fixed-focus lens can be calculated using the data in Table 1. Details of each lens are as follows.

[0049] The first lens L1 is configured as a positive lens, with a convex spherical object side with a radius of curvature of 52.401 mm, a concave spherical image side with a radius of curvature of 283.540 mm, a central axis thickness of 9.200 mm, a refractive index of 1.85, and an Abbe number of 23.8.

[0050] The second lens L2 is configured as a biconvex spherical positive lens with an object-side radius of curvature of 34.169 mm, an image-side radius of curvature of -779.152 mm, a central axis thickness of 8.900 mm, a refractive index of 1.50, an Abbe number of 81.6, and a central axis distance of 2.731 mm from the first lens.

[0051] The third lens L3 is configured as a biconcave spherical negative lens with an object-side radius of curvature of -779.152 mm, an image-side radius of curvature of 24.851 mm, a central axis thickness of 1.500 mm, a refractive index of 1.81, and an Abbe number of 25.5. It is cemented together with the second lens L2.

[0052] The fourth lens L4 is configured as a positive lens, with a convex spherical object side with a radius of curvature of 27.005 mm, a concave spherical image side with a radius of curvature of 212.543 mm, a central axis thickness of 5.900 mm, a refractive index of 1.50, an Abbe number of 81.6, a central axis distance of 0.758 mm from the third lens L3, and a central axis distance of 2.446 mm from the fifth lens L5 in the infinity focusing state.

[0053] The fifth lens, L5, is configured as a biconcave spherical negative lens with an object-side radius of curvature of -639.895 mm, an image-side radius of curvature of 30.843 mm, a central axis thickness of 0.800 mm, a refractive index of 1.49, an Abbe number of 70.4, and a central axis distance of 13.004 mm between it and the aperture stop STO in the infinity focusing state.

[0054] The sixth lens, L6, is configured as a negative lens. Its object side is a convex spherical surface with a radius of curvature of 80.800 mm, and its image side is a concave spherical surface with a radius of curvature of 27.136 mm. Its central axis thickness is 1.200 mm, its refractive index is 1.85, its Abbe number is 32.3, and its central axis distance from the aperture stop STO is 1.500 mm.

[0055] The seventh lens, L7, is a positive lens with a concave spherical object side with a radius of curvature of 27.136 mm and an image side with a concave spherical object side with a radius of curvature of 165.873 mm. It has a central axis thickness of 4.000 mm, a refractive index of 1.59, and an Abbe number of 68.3. It is cemented together with the sixth lens, L6.

[0056] The eighth lens, L8, is configured as a biconvex spherical positive lens with an object-side radius of curvature of 32.992 mm, an image-side radius of curvature of -78.979 mm, a central axis thickness of 5.400 mm, a refractive index of 1.80, an Abbe number of 42.3, and a central axis distance of 4.912 mm from that of the seventh lens, L7.

[0057] The ninth lens, L9, is configured as a biconcave spherical negative lens with an object-side radius of curvature of -182.653 mm, an image-side radius of curvature of 36.326 mm, a central axis thickness of 1.000 mm, a refractive index of 1.81, an Abbe number of 25.5, and a central axis distance of 0.150 mm from the eighth lens, L8.

[0058] The tenth lens, L10, is configured as a biconvex spherical positive lens with an object-side radius of curvature of 48.375 mm, an image-side radius of curvature of -41.288 mm, a central axis thickness of 7.000 mm, a refractive index of 1.81, an Abbe number of 25.5, and a central axis distance of 8.209 mm from the ninth lens, L9.

[0059] The eleventh lens, L11, is configured as a biconcave spherical negative lens with an object-side radius of curvature of -41.288 mm, an image-side radius of curvature of 75.906 mm, a central axis thickness of 1.500 mm, a refractive index of 1.50, and an Abbe number of 81.6. It is cemented together with the tenth lens, L10.

[0060] The twelfth lens, L12, is configured as a negative lens. Its object side is a concave spherical surface with a radius of curvature of -24.250 mm, and its image side is a convex spherical surface with a radius of curvature of -65.604 mm. Its central axis thickness is 1.000 mm, its refractive index is 1.55, and its Abbe number is 45.8. The distance between its central axis and that of the eleventh lens, L11, is 6.889 mm. In use, the distance between its central axis and that of the image plane IMG is approximately 16.0 mm.

[0061] For the spherical aberration curves along the perpendicular axis (i.e., radial and Y-axis directions) of this fixed-focus lens under the following conditions: incident light mixing range of 425~658nm, incident pupil radius of 22.7618mm, aperture of F / 1.8, and infinity focus. Figure 3a Please refer to the calculated vertical color difference curve. Figure 3b . Figure 3a The spherical aberration of all curves is in the range of -0.02 to 0.08 mm. Figure 3b The color difference of all curves is in the range of -4.5 to 3.0 micrometers.

[0062] Please see Figure 4a and Figure 4b The diagram shows the modulation transfer function (MTF) curve of the fixed-focus lens calculated under the above conditions. Figure 4aIt can be seen that the MTF values ​​of each curve decrease relatively uniformly within the frequency range of 0~30 lp / mm. Many of the upper curves are distributed within a relatively narrow ordinate range, with only the 21.6 mm-sagittal curve eventually dropping below 0.3, while the 21.6 mm-meridian curve eventually drops to 0.55. From... Figure 4b It can be seen that the image quality of this fixed-focus lens at an aperture of F / 1.8 can meet the requirements of a full-frame camera.

[0063] This fixed-focus lens has three cemented lenses. The positive and negative lenses of the cemented lenses have a large difference in dispersion coefficient, which can correct axial chromatic aberration, spherical aberration, and distortion aberration, reduce the tolerance sensitivity of image quality, and facilitate manufacturing and assembly.

[0064] In this fixed-focus lens, the first lens group G1 sequentially includes a meniscus positive lens, a cemented doublet with an approximately flat cemented surface, and another meniscus positive lens; the movable second lens group contains only one negative lens with a focal length that is 0.7 times the total focal length of the fixed-focus lens; and the third lens group sequentially includes a cemented doublet, a biconvex spherical positive lens, a biconcave spherical negative lens, another cemented doublet, and another meniscus negative lens. This fixed-focus lens can be used in full-frame cameras, does not contain aspherical elements, and has low manufacturing costs.

[0065] As a replaceable component for full-frame cameras, especially mirrorless cameras, for other aspects of the structure and function of this fixed-focus lens, please refer to paragraphs 0110 to 0122 on pages 10-11 of the specification of patent CN10847825A, or refer to commercially available camera fixed-focus lenses.

[0066] In other embodiments, the lens can be made of other types of optical materials, the stepper motor can be replaced by a voice coil motor or an ultrasonic motor, and the total focal length of the fixed-focus lens can be any value within the range of 80-90mm. Based on the lens data of Embodiment 1, the surface shape, central axis thickness, and central axis spacing of each lens can be adaptively adjusted to achieve clear imaging and other technical requirements of the camera. Specifically:

[0067] The first lens L1 has a refractive index of 1.80~1.90 and an Abbe number of 21.0~26.0;

[0068] The second lens L2, the fourth lens L4, and the eleventh lens L11 all have Abbe numbers greater than 80.0 and refractive indices in the range of 1.75 to 1.85. Preferably, the three lenses have the same Abbe number and refractive index, and more preferably, they use the same optical material.

[0069] The second lens has a side curvature radius of -750 ~ -800 mm;

[0070] The third lens L3, the ninth lens L9, and the tenth lens L10 all have Abbe numbers in the range of 23.0 to 28.0 and refractive indices in the range of 1.45 to 1.55. Preferably, the three lenses have the same Abbe number and refractive index, and more preferably, they use the same optical material.

[0071] The fifth lens has a refractive index of 1.45~1.55, an Abbe number of 68.0~73.0, and an absolute focal length of 0.7 times the total focal length of the fixed-focus lens.

[0072] The sixth lens has a refractive index of 1.80~1.90 and an Abbe number of 30.0~35.0.

[0073] The seventh lens, L7, has a refractive index of 1.55 to 1.65 and an Abbe number of 66.0 to 71.0.

[0074] The eighth lens, L8, has a refractive index of 1.75~1.85 and an Abbe number of 40.0~45.0.

[0075] The twelfth lens, L12, has a refractive index of 1.50~1.60 and an Abbe number of 43.0~48.0.

[0076] The distance between the central axes of the third lens L3 and the fourth lens L4 is less than 1.0 mm, and the distance between the central axes of the eighth lens L8 and the ninth lens L9 is 0.15 mm.

[0077] All the embodiments, application examples, and technical analyses described above are intended to introduce the technical concept and features of this utility model, enabling those skilled in the art to implement the technical solution of this utility model, and do not constitute any limitation on the scope of protection of this utility model. Simple modifications and equivalent transformations to the above embodiments are all within the scope of protection of the claims of this utility model.

Claims

1. A fixed focus lens, which can be used in a full-frame camera, comprising a first lens group with positive refractive power, a second lens group with negative refractive power and a third lens group with positive refractive power arranged in sequence along the central axis direction, and further comprising an aperture stop, when focusing from infinity to a close distance, the first lens group, the aperture stop and the third lens group are fixed relative to the image plane, and the second lens group moves along the central axis to the image plane; characterized in that The first lens group comprises, in sequence along the central axis direction: a first lens configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; a second lens configured as a biconvex positive lens, with a radius of curvature of the image side of -750 ~ -800 mm and an Abbe number greater than 80.0; a third lens configured as a biconcave negative lens, which is cemented with the second lens, with an Abbe number of 23.0 ~ 28.0; and a fourth lens configured as a positive lens, with a convex spherical surface on the object side and a concave spherical surface on the image side, with a central axis spacing of less than 1.0 mm from the third lens, and with an Abbe number greater than 80.0; wherein the second lens group only includes a fifth lens, which is a biconcave negative lens and has an absolute value of focal length of 0.7 times the total focal length of the fixed focus lens; wherein the third lens group comprises, in sequence along the central axis direction: a sixth lens configured as a negative lens, with a convex spherical surface on the object side and a concave spherical surface on the image side; a seventh lens configured as a positive lens, which is cemented with the sixth lens, with a concave spherical surface on the image side; an eighth lens configured as a biconvex positive lens; a ninth lens configured as a biconcave negative lens, with a central axis spacing of 0.15 mm from the eighth lens, and with an Abbe number of 23.0 ~ 28.0; a tenth lens configured as a biconvex positive lens, with an Abbe number of 23.0 ~ 28.0; an eleventh lens configured as a biconcave negative lens, which is cemented with the tenth lens, with an Abbe number greater than 80.0; and a twelfth lens configured as a negative lens, with a concave spherical surface on the object side and a convex spherical surface on the image side.

2. The fixed focus lens of claim 1, wherein The total focal length of the fixed focus lens is 75 ~ 85 mm. 3.The fixed focus lens according to claim 2, wherein the second lens, the fourth lens and the eleventh lens have consistent Abbe numbers and refractive indices; the third lens, the ninth lens and the tenth lens have consistent Abbe numbers and refractive indices. 4.The fixed focus lens according to claim 3, wherein the first lens has a radius of curvature of 52.401 mm on the object side, a radius of curvature of 283.540 mm on the image side, a central axis thickness of 9.200 mm, a refractive index of 1.85 and an Abbe number of 23.8; the second lens has a radius of curvature of 34.169 mm on the object side, a radius of curvature of -779.152 mm on the image side, a central axis thickness of 8.900 mm, a refractive index of 1.50 and an Abbe number of 81.6; the third lens has a radius of curvature of -779.152 mm on the object side, a radius of curvature of 24.851 mm on the image side, a central axis thickness of 1.500 mm, a refractive index of 1.81 and an Abbe number of 25.

5. The fourth lens has an object-side radius of curvature of 27.005 mm, an image-side radius of curvature of 212.543 mm, and a central axial thickness of 5.900 mm.

5. The fixed focus lens of claim 4, wherein, The sixth lens has an object-side radius of curvature of 80.800 mm, an image-side radius of curvature of 27.136 mm, a central axial thickness of 1.200 mm, a refractive index of 1.85, and an Abbe number of 32.

3. The seventh lens has an object-side radius of curvature of 27.136 mm, an image-side radius of curvature of 165.873 mm, a central axial thickness of 4.000 mm, a refractive index of 1.59, and an Abbe number of 68.

3. The eighth lens has an object-side radius of curvature of 32.992 mm, an image-side radius of curvature of -78.979 mm, a central axial thickness of 5.400 mm, a refractive index of 1.80, and an Abbe number of 42.

3. The ninth lens has an object-side radius of curvature of -182.653 mm, an image-side radius of curvature of 36.326 mm, and a central axial thickness of 1.000 mm. The tenth lens has an object-side radius of curvature of 48.375 mm, an image-side radius of curvature of -41.288 mm, and a central axial thickness of 7.000 mm. The eleventh lens has an object-side radius of curvature of -41.288 mm, an image-side radius of curvature of 75.906 mm, and a central axial thickness of 1.500 mm. The twelfth lens has an object-side radius of curvature of -24.250 mm, an image-side radius of curvature of -65.604 mm, a central axial thickness of 1.000 mm, a refractive index of 1.55, and an Abbe number of 45.

8.

6. The fixed focus lens of claim 5, wherein, The fifth lens has an object-side radius of curvature of -639.895 mm, an image-side radius of curvature of 30.843 mm, a central axial thickness of 0.800 mm, a refractive index of 1.49, and an Abbe number of 70.

4.

7. The fixed focus lens of claim 6, wherein, The aperture stop is disposed between the second lens group and the third lens group.

Images