Photographic lens

Abstract

A compact photographic lens for a digital camera is disclosed. The photographic lens has only two lens elements, yet provides excellent imaging even at the periphery of the image field. The photographic lens of the invention and an image sensor, together, fit within a volume of about 10 cm 3 . The lens is formed of, in order from the object side, a biconvex lens element having two aspherical surfaces, and a negative meniscus lens element having two aspherical surfaces. The convex surface of the meniscus lens element is positioned on the image side, and various conditions are satisfied in order to provide the photographic lens with a short overall length while favorably correcting various aberrations.

1. A photographic lens having only two lens elements, said photographic lens comprising, in order from the object side:
 a biconvex lens element having two aspherical surfaces; and 
 a negative meniscus lens element having two aspherical surfaces and with its convex surface on the image side; 
 
       wherein the following Conditions (1) and (2) are satisfied:
   2·dd 2 <dd 1    Condition (1)
 
   R 3 >R 4    Condition (2)
 
 
       where,
 dd 1  is the on-axis distance between the object-side surface and the image-side surface of the biconvex lens element, 
 dd 2  is the on-axis distance between the image-side surface of the biconvex lens element and the object-side surface of the negative meniscus lens element, 
 R 3  is the absolute value of the radius of curvature of the image-side surface of the biconvex lens element, and 
 R 4  is the absolute value of the radius of curvature of the object-side surface of the meniscus lens element. 
 
     
     
       2. The photographic lens as described in  claim 1 , wherein the image-side aspherical surface of the negative meniscus lens element is shaped so that the positive a refractive power of the image-side aspherical surface of this lens element becomes weaker towards the periphery of the lens element. 
     
     
       3. The photographic lens described in  claim 1 , wherein the following Conditions (3) and (4) are also satisfied:
   nd 1 >50νd1>50   Condition (3)
 
   νd 2 <35   Condition (4)
 
 
       where
 νd 1  is the Abbe number at the d line of the biconvex lens element, and 
 νd 2  is the Abbe number at the d line of the meniscus lens element. 
 
     
     
       4. The photographic lens described in  claim 2 , wherein the following Conditions (3) and (4) are also satisfied:
   νd 1 >50   Condition (3)
 
   νd 2 <35   Condition (4)
 
 
       where
 νd 1  is the Abbe number at the d line of the biconvex lens element, and 
 νd 2  is the Abbe number at the d line of the meniscus lens element. 
 
     
     
       5. A photographic lens having only two lens elements, said photographic lens comprising, in order from the object side:
 a biconvex lens element having two aspherical surfaces; and   a meniscus lens element having two aspherical surfaces and with its convex surface on the image side;   
       wherein the following Conditions (1) and (2) are satisfied:
   2·dd2<dd1   Condition (1)
 
   |R3|>|R4|  Condition (2)
 
 
       where,
 dd1 is the on-axis distance between the object-side surface and the image-side surface of the biconvex lens element, 
 dd2 is the on-axis distance between the image-side surface of the biconvex lens element and the object-side surface of the meniscus lens element, 
 |R3| is the absolute value of the radius of curvature of the image-side surface of the biconvex lens element, and 
 |R4| is the absolute value of the radius of curvature of the object-side surface of the meniscus lens element.  
 
     
     
       6. The photographic lens as described in claim 5, wherein the meniscus lens has a negative refractive power.  
     
     
       7. The photographic lens as described in claim 5, wherein the image-side aspherical surface of the meniscus lens element is shaped so that a refractive power of the image-side aspherical surface of this lens element becomes weaker towards the periphery of the lens element.  
     
     
       8. The photographic lens described in claim 5, wherein the following Conditions (3) and (4) are also satisfied:
   νd1>50   Condition (3)
     νd2<35   Condition (4)
   
       where
 νd1 is the Abbe number at the d line of the biconvex lens element, and 
 νd2 is the Abbe number at the d line of the meniscus lens element.  
 
     
     
       9. The photographic lens described in claim 7, wherein the following Conditions (3) and (4) are also satisfied:
   νd1>50   Condition (3)
     νd2<35   Condition (4)
   
       where
 νd1 is the Abbe number at the d line of the biconvex lens element, and 
 νd2 is the Abbe number at the d line of the meniscus lens element.  
 
     
     
       10. The photographic lens described in claim 5, wherein the following conditions are also satisfied:
   νd1>50
     νd2>=35
   
       where
 νd1 is the Abbe number at the d line of the biconvex lens element, and 
 νd2 is the Abbe number at the d line of the meniscus lens element.  
 
     
     
       11. The photographic lens described in claim 7, wherein the following conditions are also satisfied:
   νd1>50
     νd2>=35
   
       where
 νd1 is the Abbe number at the d line of the biconvex lens element, and 
 νd2 is the Abbe number at the d line of the meniscus lens element.