fig1 includes a schematic block diagram of a capsule endoscope , according to some exemplary embodiments . referring to fig1 , capsule endoscope 5 includes a sealed body 7 in which are contained a large - field - of - view lens module 10 , according to some exemplary embodiments described in detail herein . light 11 returning from an object or scene being imaged , which can be illuminated by lamps 50 , passes through a transparent portion 9 of sealed body 7 and impinges on lens module 10 . lens module 10 forms an image on image sensor 22 , which converts the received light into electrical signals and transmits them to a main processing unit 24 . main processing unit 24 processes the electrical signals to obtain digital image signals , which may be encoded and transmitted by a wireless transceiver 30 , or may be read by other means . all of these subsystems are powered as necessary by a power unit 40 , which can include one or more suitable batteries and / or power conditioning / amplifying circuits , as required . it should be noted that the capsule endoscope configuration illustrated in fig1 is intended to be exemplary only . the present disclosure is applicable to any configuration of capsule endoscope . as noted above , because of the unique environment in which capsule endoscopes are typically used , including the relatively short time available to gather image data , and the possibility of inconvenient or non - optimal capsule positioning , it is very important that the endoscope be outfitted with high - quality , wide - angle , large - field - of - view optics to increase the possibility of obtaining desirable images . in accordance with exemplary embodiments , it is desirable that the optics of the capsule endoscope comply with at least the following specific exemplary requirements : ( 1 ) large field of view ( fov ), e . g ., larger than 110 °, ( 2 ) compact size , e . g ., on the order of 1 . 2 mm × 1 . 2 mm × 2 . 1 mm , including the image plane , ( 3 ) low cost , e . g ., including no more than three lens elements in the lens system , and ( 4 ) good optical quality , e . g ., having nominal aberrations . fig2 includes a schematic block diagram of a large - field - of - view lens module , which can be used with a capsule endoscope , according to some exemplary embodiments . referring to fig2 , lens module 100 meets at least the four requirements listed above for the large - field - of - view lens module 10 . lens module 100 includes a first substrate 102 , a first lens 104 , a second lens 106 , a second substrate 108 , and a third lens 110 . in addition , lens module 100 includes two glass plates 112 and 114 in front of an image plane 116 . first substrate 102 includes two parallel planar surfaces . a first planar surface of first substrate 102 faces toward object space . first lens 104 has a planar surface ( radius r1 =∞), which is in contact with the second planar surface of first substrate 102 . first lens 104 also has a concave aspheric surface 118 , which has a radius r2 . first substrate 102 and first lens 104 collect incident rays with large incident angles entering lens module 100 . planar - concave first lens 104 mitigates the angle of incident rays that enter module 100 , reduces distortion , and reduces the cross - section of the incident rays in module 100 . second lens 106 has a convex aspheric surface 120 having radius r3 facing first lens 104 and a planar surface ( radius r4 =∞). second lens 106 is separated from first lens 104 by a predetermined distance . the predetermined distance between the center of curvature of aspheric surface 118 of first lens 104 and the center of curvature of aspheric surface 120 of second lens 106 defines a “ gap ” identified in fig2 by reference numeral 122 between aspheric surface 118 of lens 104 and aspheric surface 120 of second lens 106 . in some exemplary embodiments , the medium in gap 122 between first lens 104 and second lens 106 is air . the planar surface of second lens 106 is in contact with second substrate 108 , which has two parallel planar surfaces . second lens 106 conveys the light rays onto a stop 124 of lens module 100 . third lens 110 has a planar surface ( radius r5 =∞) in contact with second substrate 108 and a convex aspheric surface 126 having a radius r6 . second substrate 108 is thus sandwiched between second lens 106 and third lens 110 . stop 124 is interposed between second substrate 108 and third lens 110 . third lens 110 leads light rays to arrive at image plane 116 through two glass plates 112 and 114 . glass plates 112 and 114 may be separated by a small distance . glass plate 114 may be the cover glass of an image sensor . glass plate 114 and image plane 116 may be separated by a small distance . stop 124 located within lens module 100 helps to maintain cones of rays in the field of view symmetric . this in turn helps to maintain the symmetric performance of the modulation transfer function ( mtf ). table 1 shows the lens data of lens module 100 according to the exemplary embodiments illustrated in fig2 . v1 , v2 , and v3 are the abbe numbers of first lens 104 , second lens 106 , and third lens 110 , respectively . abs denotes the absolute value . r2 , r3 , and r6 are the radii of the aspheric surfaces of first lens 104 , second lens 106 , and third lens 110 , respectively . gap is the distance from the center of curvature of aspheric surface 118 of first lens 104 to the center of curvature of aspheric surface 120 of second lens 106 . fig3 ( a ), 3 ( b ), 3 ( c ), and 3 ( d ) are curves which illustrate spherical aberration , field curvature , distortion , and lateral color aberration , respectively , for lens module 100 illustrated in fig2 , according to some exemplary embodiments . referring to fig3 ( a ), the three curves , from left to right , correspond to light with wavelengths of 435 . 8 nm ( f curve ), 587 . 6 nm ( d curve ), and 656 . 3 nm ( c curve ). the spherical aberration is in a possible range which is illustrated to extend from − 0 . 10 mm to 0 . 10 mm . referring to the diagram of fig3 ( b ), the field curvature is in a possible range which is illustrated to extend from − 0 . 10 mm to 0 . 10 mm . referring to the diagram of fig3 ( c ), the distortion is in a possible range which is illustrated to extend from − 50 % to 50 %. referring to the diagram of fig3 ( d ), the lateral color aberration is limited within an airy disk from − 5 . 00 μm to 5 . 00 μm . the aberration values are nominal as understood by those of ordinary skill in the art . in some exemplary embodiments , the dimensions of the optics part of lens module 100 that includes first substrate 102 , first lens 104 , second lens 106 , second substrate 108 , and third lens 110 are approximately 1 . 04 mm × 1 . 04 mm × 1 . 12 mm for an overall volume of approximately 1 . 21 mm 3 the total length from the outer surface of the first substrate to the image plane is approximately 2 . 085 mm , which is less than 2 . 2 mm . in some exemplary embodiments , lens module 100 uses two substrates and three lens elements . for example , the exemplary embodiments illustrated in fig2 meet the four specific exemplary requirements : ( 1 ) large field - of - view ( fov ) of about 118 °, ( 2 ) imaging optics compact size of about 1 . 04 × 1 . 04 × 2 . 085 mm ( size of the first substrate × total length ), ( 3 ) low cost since it comprises only three lens elements , and ( 4 ) good optical quality of nominal aberration . it is understood that the invention may not be limited by these four exemplary specifications . in some exemplary embodiments , the focal length of lens module 100 is 0 . 4 mm , which is less than 0 . 43 mm , and the f - number is 4 . in some exemplary embodiments , the diameter of rays at the image plane is 0 . 938 mm , which is less than 1 mm . in some exemplary embodiments the conic values of the aspheric surfaces of first lens 104 , second lens 106 , and third lens 110 are zero . fig4 includes a schematic block diagram of a large - field - of - view lens module , which can be used with a capsule endoscope , according to some other exemplary embodiments . referring to fig4 , lens module 200 also meets at least the four requirements listed above for the large - field - of - view lens module 10 . lens module 200 includes a first substrate 202 , a first lens 204 , a second lens 206 , a second substrate 208 , and a third lens 210 . in addition , lens module 200 includes a glass plate 214 in front of an image plane 216 . first substrate 202 includes two parallel planar surfaces . a first planar surface of first substrate 202 faces toward object space . first lens 204 has a planar surface ( radius r1 =∞), which is in contact with the second planar surface of first substrate 202 . first lens 204 also has a concave aspheric surface 218 , which has a radius r2 . second lens 206 has a convex aspheric surface 220 having radius r3 facing first lens 204 and a planar surface ( radius r4 =∞). second lens 206 is separated from first lens 204 by a predetermined distance . the predetermined distance between the center of curvature of aspheric surface 218 of first lens 204 and the center of curvature of aspheric surface 220 of second lens 206 defines a “ gap ” identified in fig2 by reference numeral 222 between aspheric surface 218 of lens 204 and aspheric surface 220 of second lens 206 . in some exemplary embodiments , the medium in gap 222 between first lens 204 and second lens 206 is air . the planar surface of second lens 206 is in contact with second substrate 208 , which has two parallel planar surfaces . third lens 210 has a planar surface ( radius r5 =∞) in contact with second substrate 208 and a convex aspheric surface 226 having a radius r6 . second substrate 208 is thus sandwiched between second lens 206 and third lens 210 . stop 224 is interposed between second substrate 208 and third lens 210 . third lens 210 leads light rays to arrive at image plane 216 through glass plate 114 . glass plate 214 may be the cover glass of an image sensor . glass plate 214 and image plane 216 may be separated by a distance . stop 224 located within lens module 200 helps to maintain cones of rays in the field of view symmetric . this in turn helps to maintain the symmetric performance of the modulation transfer function ( mtf ). table 2 shows the lens data of lens module 200 according to the exemplary embodiments illustrated in fig4 . fig5 ( a ), 5 ( b ), 5 ( c ), and 5 ( d ) are curves which illustrate spherical aberration , field curvature , distortion , and lateral color aberration , respectively , for lens module 200 illustrated in fig4 , according to some exemplary embodiments . referring to fig5 ( a ), the three curves , from left to right , correspond to light with wavelengths of 435 . 8 nm ( f curve ), 587 . 6 nm ( d curve ), and 656 . 3 nm ( c curve ). the spherical aberration is in a possible range which is illustrated to extend from − 0 . 05 mm to 0 . 05 mm . referring to the diagram of fig5 ( b ), the field curvature is in a possible range which is illustrated to extend from − 0 . 10 mm to 0 . 10 mm . referring to the diagram of fig5 ( c ), the distortion is in a possible range which is illustrated to extend from − 50 % to 50 %. referring to the diagram of fig5 ( d ), the lateral color aberration is limited within an airy disk from − 5 . 00 μm to 5 . 00 μm . the aberration values are nominal as understood by those of ordinary skill in the art . in some exemplary embodiments , the dimensions of the optics part of lens module 200 that includes first substrate 202 , first lens 204 , second lens 206 , second substrate 208 , and third lens 210 are approximately 1 . 18 mm × 1 . 18 mm × 1 . 261 mm for an overall volume of approximately 1 . 76 mm 3 . the total length from the outer surface of the first substrate to the image plane is approximately 1 . 94 mm . in some exemplary embodiments , lens module 200 uses two substrates and three lens elements . for example , the exemplary embodiments illustrated in fig4 meet the four specific exemplary requirements : ( 1 ) large field - of - view ( fov ) of about 115 °, ( 2 ) imaging optics compact size of about 1 . 18 × 1 . 18 × 1 . 94 mm ( size of the first substrate × total length ), ( 3 ) low cost since it comprises only three lens elements , and ( 4 ) good optical quality of nominal aberration . it is understood that the invention may not be limited by these four exemplary specifications . in some exemplary embodiments , the focal length of lens module 200 is approximately 0 . 43 mm , and the f - number is 3 . 8 , which is less than 4 . in some exemplary embodiments , the diameter of rays at the image plane is 0 . 885 mm , which is less than 1 mm . in some exemplary embodiments the conic values of the aspheric surfaces of first lens 204 , second lens 206 , and third lens 210 are zero . various features of the present disclosure have been described above in detail . the disclosure covers any and all combinations of any number of the features described herein , unless the description specifically excludes a combination of features . the following examples illustrate some of the combinations of features contemplated and disclosed herein in accordance with this disclosure . in any of the embodiments described in detail and / or claimed herein , a stop may be interposed between the second substrate and the third lens . in any of the embodiments described in detail and / or claimed herein , a field of view of the lens system may be greater than 110 °. in any of the embodiments described in detail and / or claimed herein , a total length of the lens system from an outer surface of the first substrate to an image plane may be less than 2 . 1 mm . in any of the embodiments described in detail and / or claimed herein , a focal length of the lens system may be equal to or less than 0 . 43 mm . in any of the embodiments described in detail and / or claimed herein , an f - number of the lens system may be equal to or less than 4 . in any of the embodiments described in detail and / or claimed herein , a diameter of light rays at an image plane of the lens system may be less than 1 . 0 mm . in any of the embodiments described in detail and / or claimed herein , each of the first substrate and the second substrate may have two parallel planar surfaces . in any of the embodiments described in detail and / or claimed herein , the lens system may be contained within a capsule endoscope . while the present disclosure has shown and described exemplary embodiments , it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure , as defined by the following claims .