Compact optical system, image capturing unit and electronic device

Abstract

A compact optical system includes, in order from an object side to an image side, a first lens element, a second lens element and a third lens element. The first lens element with negative refractive power has an image-side surface being concave in a paraxial region thereof. The second lens element has refractive power, wherein at least one of two surfaces of the second lens element is aspheric, and the second lens element is made of plastic material. The third lens element has positive refractive power, wherein at least one of two surfaces of the third lens element is aspheric, and the third lens element is made of plastic material. The compact optical system further comprises a stop located between the first lens element and the second lens element. The first, second, and third lens elements are all stationary relative to one another in a paraxial region.

What is claimed is: 
     
       1. A compact optical system comprising, in order from an object side to an image side:
 a first lens element with negative refractive power having an image-side surface being concave in a paraxial region thereof; 
 a second lens element, wherein at least one of an object-side surface and an image-side surface of the second lens element is aspheric, and the second lens element is made of plastic material; and 
 a third lens element having positive refractive power, wherein at least one of an object-side surface and an image-side surface of the third lens element is aspheric, and the third lens element is made of plastic material; 
 wherein the compact optical system has a total of three lens elements, the compact optical system further comprises an aperture stop located between the first lens element and the second lens element, the first lens element, the second lens element and the third lens element are all stationary relative to one another in a paraxial region thereof; 
 wherein a focal length of the compact optical system is f, a maximum image height of the compact optical system is ImgH, an entrance pupil diameter of the compact optical system is EPD, a refractive index of the first lens element is N1, a refractive index of the second lens element is N2, a refractive index of the third lens element is N3, an axial distance between the aperture stop and the object-side surface of the second lens element is Dsr3, an axial distance between the aperture stop and the object-side surface of the third lens element is Dsr5, and the following conditions are satisfied:
   f/ImgH<0.55; 
   f/EPD<2.60; 
   4.70<N1+N2+N3<5.50; and 
   0<|Dsr3/Dsr5|<0.50. 
 
 
     
     
       2. The compact optical system of  claim 1 , wherein the image-side surface of the third lens element is convex in a paraxial region thereof. 
     
     
       3. The compact optical system of  claim 2 , wherein the second lens element has positive refractive power, and the image-side surface of the second lens element is convex in a paraxial region thereof. 
     
     
       4. The compact optical system of  claim 2 , wherein a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:
   −0.50<(R5+R6)/(R5−R6)<0.50.
 
 
     
     
       5. The compact optical system of  claim 1 , wherein at least one of the object-side surface and the image-side surface of the third lens element has at least one inflection point, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:
   (R5+R6)/(R5−R6)<0.90.
 
 
     
     
       6. The compact optical system of  claim 1 , wherein an axial distance between an imaged object and an image surface is OTL, and the following condition is satisfied:
 OTL21 8.0 millimeters (mm). 
 
     
     
       7. The compact optical system of  claim 1 , wherein the focal length of the compact optical system is f, the maximum image height of the compact optical system is ImgH, and the following condition is satisfied:
   f/ImgH<0.45. 
 
     
     
       8. The compact optical system of  claim 1 , wherein an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, an Abbe number of the third lens element is V3, and the following condition is satisfied:
   V1+V2+V3<80. 
 
     
     
       9. The compact optical system of  claim 1 , further comprising a flat panel, wherein the flat panel is located between so an imaged object and an object-side surface of the first lens element. 
     
     
       10. An image capturing unit, comprising:
 the compact optical system of  claim 1 ; and 
 an image sensor, wherein the image sensor is disposed on the image side of the compact optical system. 
 
     
     
       11. An electronic device comprising:
 a biometric system, wherein the biometric system comprises the image capturing unit of  claim 10 . 
 
     
     
       12. A compact optical system comprising, in order from an object side to an image side:
 a first lens element with negative refractive power having an image-side surface being concave in a paraxial region thereof; 
 a second lens element, wherein at least one of an object-side surface and an image-side surface of the second lens element is aspheric, and the second lens element is made of plastic material; and 
 a third lens element having positive refractive power, wherein at least one of an object-side surface and an image-side surface of the third lens element is aspheric, and the third lens element is made of plastic material; 
 wherein the compact optical system has a total of three lens elements, the compact optical system further comprises an aperture stop located between the first lens element and the second lens element, the first lens element, the second lens element and the third lens element are all stationary relative to one another in a paraxial region thereof; 
 wherein a focal length of the compact optical system is f, a focal length of the first lens element is f1, a focal length of the second lens element is f2, a focal length of the third lens element is f3, a maximum image height of the compact optical system is ImgH, a refractive index of the first lens element is N1, a refractive index of the second lens element is N2, a refractive index of the third lens element is N3, an axial distance between the aperture stop and the object-side surface of the second lens element is Dsr3, an axial distance between the aperture stop and the object-side surface of the third lens element is Dsr5, an axial distance between an imaged object and an image surface is OTL, a sum of central thicknesses of the first lens element, the second lens element and the third lens element is ΣCT, and the following conditions are satisfied:
   0.5<|f/f1|+|f/f2|+|f/f3|<1.1; 
   f/ImgH<0.70; 
   4.70<N1+N2+N3<5.50; 
   0<|Dsr3/Dsr5|<0.50; and 
   OTL/ΣCT<4.0.
 
 
 
     
     
       13. The compact optical system of  claim 12 , wherein the image-side surface of the third lens element is convex in a paraxial region thereof. 
     
     
       14. The compact optical system of  claim 12 , wherein the axial distance between the imaged object and the image surface is OTL, the maximum image height of the compact optical system is ImgH, and the following condition is satisfied:
   OTL/ImgH<12. 
 
     
     
       15. The compact optical system of  claim 14 , wherein a maximal field of view of the compact optical system is FOV, and the following condition is satisfied:
   140.0 degrees (deg.)<FOV<180.0 deg. 
 
     
     
       16. The compact optical system of  claim 14 , wherein the compact optical system further comprises a flat panel located between the imaged object and an object-side surface of the first lens element, a central thickness of the flat panel is CTf, a central thickness of the first lens element is CT1, and the following condition is satisfied:
   0.95<CTf/CT1<5.5. 
 
     
     
       17. The compact optical system of  claim 12 , wherein at least one of the object-side surface and the image-side surface of the third lens element has at least one inflection point, the axial distance between the imaged object and the image surface is OTL, and the following condition is satisfied:
   OTL<5.0 mm. 
 
     
     
       18. The compact optical system of  claim 12 , wherein a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:
   (R5+R6)/(R5−R6)<0.90.
 
 
     
     
       19. The compact optical system of  claim 12 , wherein an axial distance between the first lens element and the second lens element is T12, a central thickness of the first lens element is CT1, and the following condition is satisfied:
   1.50<T12/CT1<10. 
 
     
     
       20. The compact optical system of  claim 12 , wherein an axial distance between the imaged object and an object-side surface of the first lens element is OL, an axial distance between the object-side surface of the first lens element and the image surface is TL, and the following condition is satisfied:
   0<OL/TL<1.0. 
 
     
     
       21. The compact optical system of  claim 12 , wherein an axial distance between the object-side surface of the first lens element and the image-side surface of the third lens element is TD, the focal length of the compact optical system is f, and the following condition is satisfied:
   8<TD/f<30. 
 
     
     
       22. An image capturing unit, comprising:
 the compact optical system of  claim 12 ; 
 a light source; and 
 an image sensor, wherein the image sensor is disposed on the image side of the compact optical system. 
 
     
     
       23. The image capturing unit of  claim 22 , wherein the light source is within a wavelength range of 400 nanometers (nm) to 500 nm. 
     
     
       24. A compact optical system comprising three lens elements, the three lens elements being, in order from an object side to an image side, a first lens element, a second lens element and a third lens element; each of the three lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side;
 wherein the first lens element has negative refractive power, the object-side surface of the second lens element is convex in a paraxial region thereof, the third lens element has positive refractive power, and the object-side surface of the third lens element is convex in a paraxial region thereof;   wherein the compact optical system has a total of three lens elements, an axial distance between the first lens element and the second lens element is larger than an axial distance between the second lens element and the third lens element, an absolute value of a curvature radius of the object-side surface of the third lens element is larger than an absolute value of a curvature radius of the image-side surface of the third lens element;   wherein a focal length of the compact optical system is f, an entrance pupil diameter of the compact optical system is EPD, an axial distance between an imaged object and an image surface is OTL, and the following conditions are satisfied:
   f/EPD≤1.60; and
 
   OTL<5.0 mm.  
   
     
     
       25. The compact optical system of claim 24, wherein the object-side surface of the first lens element is concave in a paraxial region thereof.  
     
     
       26. The compact optical system of claim 24, wherein the second lens element has positive refractive power, and the image-side surface of the first lens element is concave in a paraxial region thereof.  
     
     
       27. The compact optical system of claim 24, wherein the image-side surface of the third lens element is convex in a paraxial region thereof.  
     
     
       28. The compact optical system of claim 24, wherein at least one of the object-side surface and the image-side surface of the third lens element has at least one inflection point.  
     
     
       29. The compact optical system of claim 24, wherein each of the first lens element, the second lens element and the third lens element is made of plastic material, the curvature radius of the object-side surface of the third lens element is R5, the curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:
   (R5+R6)/(R5−R6)<0.90. 
   
     
     
       30. The compact optical system of claim 24, wherein the axial distance between the imaged object and the image surface is OTL, a sum of central thicknesses of the first lens element, the second lens element and the third lens element is ΣCT, and the following condition is satisfied:
   OTL/ΣCT<4.0. 
 
 
     
     
       31. The compact optical system of claim 24, further comprises a flat panel located between an imaged object and the object-side surface of the first lens element.  
     
     
       32. The compact optical system of claim 24, wherein a refractive index of the first lens element is N1, a refractive index of the second lens element is N2, a refractive index of the third lens element is N3, and the following condition is satisfied:
   4.70<N1+N2+N3<5.50.   
       
        
       
     
     
       33. An image capturing unit, comprising:
 the compact optical system of claim 24;   a barrel member; and   an image sensor, disposed on the image side of the compact optical system.    
     
     
       34. An electronic device comprising:
 a biometric system, wherein the biometric system comprises the image capturing unit of claim 33.    
     
     
       35. A compact optical system comprising three lens elements, the three lens elements being, in order from an object side to an image side, a first lens element, a second lens element and a third lens element; each of the three lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side;
 wherein the first lens element has negative refractive power, the object-side surface of the first lens element is concave in a paraxial region thereof, the first lens element is made of plastic material, the object-side surface of the second lens element is convex in a paraxial region thereof, the third lens element has positive refractive power, and the object-side surface of the third lens element is convex in a paraxial region thereof;   wherein the compact optical system has a total of three lens elements, an axial distance between the first lens element and the second lens element is larger than an axial distance between the second lens element and the third lens element, the axial distance between the first lens element and the second lens element is larger than a central thickness of the second lens element, an absolute value of a curvature radius of the object-side surface of the third lens element is larger than an absolute value of a curvature radius of the image-side surface of the third lens element;   wherein a focal length of the compact optical system is f, an entrance pupil diameter of the compact optical system is EPD, and the following condition is satisfied:
   f/EPD<2.60.  
   
     
     
       36. The compact optical system of claim 35, wherein the second lens element has positive refractive power, and the image-side surface of the first lens element is concave in a paraxial region thereof.  
     
     
       37. The compact optical system of claim 35, wherein at least one of the object-side surface and the image-side surface of the first lens element has at least one inflection point, at least one of the object-side surface and the image-side surface of the first lens element is aspheric, at least one of the object-side surface and the image-side surface of the second lens element is aspheric, at least one of the object-side surface and the image-side surface of the third lens element is aspheric, and the image-side surface of the third lens element is convex in a paraxial region thereof.  
     
     
       38. The compact optical system of claim 35, wherein the axial distance between the first lens element and the second lens element is T12, a central thickness of the first lens element is CT1, and the following condition is satisfied:
   1.50<T12/CT1<10.    
     
     
       39. The compact optical system of claim 35, wherein an axial distance between an imaged object and an image surface is OTL, a maximum image height of the compact optical system is ImgH, and the following condition is satisfied:
   OTL/ImgH<12.    
     
     
       40. The compact optical system of claim 35, further comprises a flat panel located between an imaged object and the object-side surface of the first lens element, wherein an axial distance between an imaged object and the object-side surface of the first lens element is OL, an axial distance between the object-side surface of the first lens element and an image surface is TL, and the following condition is satisfied:
   0<OL/TL<1.0.   
       
        
       
     
     
       41. The compact optical system of claim 35, wherein an absolute value of a curvature radius of the object-side surface of the first lens element is larger than an absolute value of a curvature radius of the image-side surface of the first lens element.  
     
     
       42. A compact optical system comprising three lens elements, the three lens elements being, in order from an object side to an image side, a first lens element, a second lens element and a third lens element; each of the three lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side;
 wherein the first lens element has negative refractive power, the object-side surface and the image-side surface of the first lens element are both aspheric, the object-side surface of the first lens element is concave in a paraxial region thereof and has at least one convex shape in an off-axis region thereof, at least one of the object-side surface and the image-side surface of the first lens element has at least one inflection point, the first lens element is made of plastic material, and the third lens element has positive refractive power;   wherein the compact optical system has a total of three lens elements, there is an air gap in a paraxial region between each of adjacent lens elements of the compact optical system;   wherein a focal length of the compact optical system is f, an entrance pupil diameter of the compact optical system is EPD, and the following condition is satisfied:
   f/EPD≤1.60. 
 
   
     
     
       43. The compact optical system of claim 42, wherein the object-side surface and the image-side surface of the second lens element are both aspheric, the object-side surface and the image-side surface of the third lens element are both aspheric, and the object-side surface of the first lens element is concave in a paraxial region thereof.  
     
     
       44. The compact optical system of claim 42, further comprising an aperture stop located between the first lens element and the second lens element, wherein each of the second lens element and the third lens element is made of plastic material.  
     
     
       45. The compact optical system of claim 42, further comprises a flat panel located between an imaged object and the object-side surface of the first lens element.  
     
     
       46. The compact optical system of claim 42, further comprising a glare stop located between the first lens element and the third lens element.  
     
     
       47. The compact optical system of claim 42, wherein at least one of the object-side surface and the image-side surface of the second lens element is aspheric, at least one of the object-side surface and the image-side surface of the third lens element is aspheric, an axial distance between an imaged object and an image surface is OTL, and the following condition is satisfied:
   OTL<5.0 mm.    
     
     
       48. The compact optical system of claim 42, wherein an axial distance between an imaged object and an image surface is OTL, a sum of central thicknesses of the first lens element, the second lens element and the third lens element is ΣCT, and the following condition is satisfied:
   OTL/ΣCT<4.0. 
 
 
     
     
       49. The compact optical system of claim 42, wherein the object-side surface of the second lens element is convex in a paraxial region thereof.  
     
     
       50. The compact optical system of claim 42, wherein the image-side surface of the second lens element is convex in a paraxial region thereof, an axial distance between an imaged object and an image surface is OTL, and the following condition is satisfied:
   OTL<8.0 mm.    
     
     
       51. The compact optical system of claim 42, wherein the object-side surface of the third lens element is convex in a paraxial region thereof, an axial distance between an imaged object and an image surface is OTL, a maximum image height of the compact optical system is ImgH, and the following condition is satisfied:
   OTL/ImgH<12.    
     
     
       52. The compact optical system of claim 42, further comprising an aperture stop located between the first lens element and the third lens element, wherein the image-side surface of the third lens element is convex in a paraxial region thereof.  
     
     
       53. The compact optical system of claim 42, wherein the image-side surface of the first lens element is concave in a paraxial region thereof, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, and the following condition is satisfied:
   (R5+R6)/(R5−R6)<0.90. 
   
     
     
       54. The compact optical system of claim 42, wherein at least one of the object-side surface and the image-side surface of the third lens element has at least one inflection point.  
     
     
       55. The compact optical system of claim 42, wherein the focal length of the compact optical system is f, a maximum image height of the compact optical system is ImgH, and the following condition is satisfied:
   f/ImgH<0.45.    
     
     
       56. The compact optical system of claim 42, wherein a refractive index of the first lens element is N1, a refractive index of the second lens element is N2, a refractive index of the third lens element is N3, and the following condition is satisfied:
   4.70<N1+N2+N3<5.50.    
     
     
       57. The compact optical system of claim 42, wherein a maximal field of view of the compact optical system is FOV, and the following condition is satisfied:
   140.0 deg.<FOV<180.0 deg.    
     
     
       58. The compact optical system of claim 42, further comprising an aperture stop, wherein an axial distance between the aperture stop and the object-side surface of the second lens element is Dsr3, an axial distance between the aperture stop and the object-side surface of the third lens element is Dsr5, and the following condition is satisfied:
   0<|Dsr3/Dsr5|<0.50.   
       
        
       
     
     
       59. The compact optical system of claim 42, wherein an axial distance between the first lens element and the second lens element is larger than an axial distance between the second lens element and the third lens element.  
     
     
       60. The compact optical system of claim 42, wherein a central thickness of the second lens element is larger than a central thickness of the third lens element.  
     
     
       61. The compact optical system of claim 42, wherein an absolute value of a curvature radius of the object-side surface of the second lens element is larger than an absolute value of a curvature radius of the image-side surface of the second lens element.  
     
     
       62. An image capturing unit, comprising:
 the compact optical system of claim 42;   a barrel member; and   an image sensor, disposed on the image side of the compact optical system.    
     
     
       63. An electronic device comprising:
 a biometric system, wherein the biometric system comprises the image capturing unit of claim 62.