The invention relates to an optical lens, and, more particularly, to a relay lens that can be used with a mobile device.
Nowadays, smartphones can be used for fundus photography to replace traditional ophthalmoscopes. Using a smartphone to take fundus photos may have various advantages. For example, the image pick-up device needs not to connect with a remote computer system, and the captured fundus images can be analyzed in real time. When a smartphone is used for fundus photography, it is necessary to use an adapter with a relay lens inside to match the lens of the smartphone to obtain a complete fundus image. Therefore, it is desirable to provide a relay lens that can be used with various types of mobile devices and may achieve wider viewing angles, lighter weight, lower fabrication costs, and higher imaging quality.
According to one aspect of the present disclosure, an optical lens used for fundus photography includes a first plastic aspheric lens with a positive refractive power, a second plastic aspheric lens with a refractive power, a third plastic aspheric lens with a refractive power, and a fourth plastic aspheric lens with a positive refractive power arranged in order from an object side to an image side. The first lens and the fourth lens are the outermost lenses at opposite ends of the optical lens. The number of lenses with refractive powers is less than 9, each lens of the optical lens is a singlet lens, a length between respective optical centers of outermost lens surfaces at opposite ends of the optical lens is within a range of 50 mm to 130 mm, and a back focal length is greater than 20 mm.
According to another aspect of the present disclosure, an optical lens includes a first lens, a second lens, a third lens and a fourth lens arranged in order in a direction. The first lens is an aspheric lens with a positive refractive power, the second lens is an aspheric lens with a refractive power, the third lens is an aspheric lens with a refractive power, and the fourth lens is an aspheric lens with a positive refractive power. The number of lenses with refractive powers of the optical lens is less than 9, and a full field of view (FOV) of the optical lens is within a range of 30 degrees to 55 degrees. The optical lens satisfies a condition of 0.14<D1/OAL<0.5, where D1 denotes a lens diameter of the first lens, and OAL denotes a length between respective optical centers of outermost lens surfaces at opposite ends of the optical lens.
According to the above aspects, the optical lens may have at least one of the advantages of light weight, low fabrication costs, wide viewing angles and high resolution relaying images. Therefore, the optical lens is suitable for matching various types of mobile devices complying with their respective specifications to generate high-quality fundus images.
Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention.
In the following detailed description of the preferred embodiments, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. The components of the invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. Further, “First,” “Second,” etc., as used herein, are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.).
The term “lens” refers to an element made from a partially or entirely light-transmissive material with optical power. The material commonly includes plastic or glass. The lens may be, a general lens, a prism, an aperture stop, a cylindrical lens, a bi-conical lens, a cylindrical array lens, a wedge lens, a wedge, or a combination of the foregoing elements.
When the optical lens is used for fundus photography, an image side may refer to one side of an optical path comparatively near an external imaging system (such as a smartphone), and an object side may refer to other side of the optical path comparatively near an object (such as human eyes) to be captured.
A certain region of an object side surface (or an image side surface) of a lens may be convex or concave. Herein, a convex or concave region is more outwardly convex or inwardly concave in the direction of an optical axis as compared with other neighboring regions of the object/image side surface.
According to various embodiments of the invention, the number of lenses with refractive powers is less than 9, but the number, shape and optical characteristic of lenses can be designed according to actual needs without limitation. For example, in one embodiment, the lens L3 can be replaced with two singlet lenses that are stacked together by a spacing of less than 0.05 mm and have substantially the same radius of curvature in two adjacent lens surfaces, and the two singlet lenses may respectively have a high Abbe number and a low Abbe number to facilitate chromatic aberration corrections and hence improve imaging resolution. In other embodiment, in addition to replacing the lens L3 with two singlet lenses as described above, the lens L4 can be also replaced with two singlet lenses having the specific configuration as described above. In other embodiment, the lens L3 can be replaced with three singlet lenses having the specific configuration as described above, and the three singlet lenses may respectively have a high Abbe number, a low Abbe number and a high Abbe number or respectively have a low Abbe number, a high Abbe number and a low Abbe number to facilitate chromatic aberration corrections.
In each of the following embodiments, the object side OS is located on the left side and the image side IS is located on the right side of each figure, and thus this is not repeatedly described in the following for brevity.
Detailed optical data and design parameters of the optical lens 10a are shown in Table 1 below. Note the data provided below are not used for limiting the invention, and those skilled in the art may suitably modify parameters or settings of the following embodiment with reference of the invention without departing from the scope or spirit of the invention.
Table 1 lists the values of parameters for each lens of the optical lens 10a, where the surface symbol denoted by an asterisk is an aspherical surface. Besides, the radius of curvature, thickness/interval and diameter shown in Table 1 are all in a unit of mm.
In the above Table 1, the field heading “interval” represents a distance between two adjacent surfaces along the optical axis 12 of the optical lens 10a. For example, an interval of the surface S1 is a distance between the surface S1 and the surface S2 along the optical axis 12. Further, the interval, refractive index and Abbe number of any lens listed in the column of “Object description” show values in a horizontal row aligned with the position of that lens. Moreover, in table 1, the surfaces S1 and S2 are respectively the object-side surface and image-side surface of the lens L1, the surfaces S3 and S4 are respectively the object-side surface and image-side surface of the lens L2, and the remaining lens surfaces are classified by analogy so that related descriptions are omitted for sake of brevity.
The radius (radius of curvature) in the above table is a reciprocal of the curvature. When a lens surface has a positive radius of curvature, the center of the lens surface is located towards the image side. When a lens surface has a negative radius of curvature, the center of the lens surface is located towards the object side.
According to various embodiments of the invention, a back focal length (a distance between the lens surface closest to the image side IS and the pupil 14 of the external imaging system) may be greater than 20 mm, and an overall length OAL may be within a range of 50 mm to 130 mm, preferably 55 mm to 128 mm, and more preferably 60 mm to 126 mm. Herein, two outermost lens surfaces (such as the surfaces S1 and S12 shown in
In this embodiment, a back focal length of the optical lens 10a is 20.68 mm, an overall length OAL is 114.206 mm, an effective focal length EFL is 199.609 mm, an object distance (a distance between an eye model 22 and a lens surface S1 closest to the object side OS) is 25 mm, a diameter of an entrance pupil (a pupil of the eye model) is 4 mm, and a diameter of the exit pupil 14 (an aperture stop of the external imaging system) is 2.648 mm.
FOV stands for a light collection angle of an optical surface S1 closest to the magnified side OS; that is, the FOV is a full field of view measured by a horizontal line and a vertical line. According to an embodiment of the invention, the FOV is within a range of 30 degrees to 55 degrees, preferably 32 degrees to 54 degrees, and more preferably 34 degrees to 53 degrees. In this embodiment, the full field of view FOV of the optical lens 10a is 44.189 degrees.
Each of the lenses may be assigned a parameter of “lens diameter”. For example, as shown in
An aspheric lens indicates at least one of its front lens surface and rear lens surface has a radius of curvature that varies along a center axis to correct abbreviations. In the following design examples of the invention, each aspheric surface satisfies the following equation:
where Z denotes a sag of an aspheric surface along the optical axis 12, c denotes a reciprocal of a radius of an osculating sphere, K denotes a Conic constant, r denotes a height of the aspheric surface measured in a direction perpendicular to the optical axis 12, and parameters A-I listed in Table 2 are 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th and 20th order aspheric coefficients. Note the data provided below are not used for limiting the invention, and those skilled in the art may suitably modify parameters or settings of the following embodiment with reference of the invention without departing from the scope or spirit of the invention.
In the embodiment of
According to various embodiments of the invention, by using a large number of plastic aspheric lenses, fabrication costs can be reduced without lowering imaging qualities. In addition, the optical lens may consist essentially of less than 9 lenses and does not have any cemented lens, this may help to reduce fabrication costs and overall weight. Through the design of the various embodiments, the optical lens may have at least one of the following advantages: light weight, low fabrication costs, wide viewing angles and high-resolution relaying images. Therefore, the optical lens is suitable for matching various types of mobile devices complying with their respective specifications to generate high-quality fundus images.
Though the embodiments of the invention have been presented for purposes of illustration and description, they are not intended to be exhaustive or to limit the invention. Accordingly, many modifications and variations without departing from the spirit of the invention or essential characteristics thereof will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated.
Number | Date | Country | Kind |
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111118522 | May 2022 | TW | national |