Single focus lens
View Patent ↗A single focus lens is disclosed that is formed of only four lens elements. In order from the object side, these are: a first lens element of positive refractive power and having either a concave surface or planar surface on the object side; a second lens element of weak refractive power and meniscus shape that is made of plastic with at least one surface aspheric; a third lens element which has positive refractive power and a convex surface on the image side; and a fourth lens element of weak refractive power and meniscus shape that is made of plastic with at least one surface aspheric and with its concave surface on the image side. Preferably, various conditions are satisfied in order that the single focus lens be compact and favorably correct aberrations so as to provide a high quality image.
1. A single focus lens that is formed of only four lens elements, said single focus lens comprising, in order from the object side: a first lens element of positive refractive power and having either a concave surface or planar surface on the object side; a second lens element of weak refractive power that is made of plastic with at least one surface aspheric and which has a meniscus shape; a third lens element which has a positive refractive power and a convex surface on the image side; and a fourth lens element of weak refractive power that is made of plastic with at least one surface aspheric and which has a meniscus shape with its concave surface on the image side.
2. The single focus lens according to claim 1 , wherein the object-side surface of the third lens element is concave.
3. The single focus lens according to claim 1 , wherein a diaphragm stop is arranged between the second lens element and the third lens element.
4. The single focus lens according to claim 2 , wherein a diaphragm stop is arranged between the second lens element and the third lens element.
5. The single focus lens according to claim 1 , wherein the following Conditions (1), (2) and (3) are satisfied:
−0.2 <f/f 2 <0.2 Condition (1)
−0.2 <f/f 4 <0.2 Condition (2)
f 1 /f 3 >2 Condition (3)
where
f is the focal length of the single focus lens,
f 1 is the focal length of the first lens element, in order from the object side,
f 2 is the focal length of the second lens element, in order from the object side,
f 3 is the focal length of the third lens element, in order from the object side, and
f 4 is the focal length of the fourth lens element, in order from the object side.
6. The single focus lens according to claim 2 , wherein the following Conditions (1), (2) and (3) are satisfied:
−0.2 <f/f 2 <0.2 Condition (1)
−0.2 <f/f 4 <0.2 Condition (2)
f 1 /f 3 >2 Condition (3)
where
f is the focal length of the single focus lens,
f 1 is the focal length of the first lens element, in order from the object side,
f 2 is the focal length of the second lens element, in order from the object side,
f 3 is the focal length of the third lens element, in order from the object side, and
f 4 is the focal length of the fourth lens element, in order from the object side.
7. The single focus lens according to claim 3 , wherein the following Conditions (1), (2) and (3) are satisfied:
−0.2 <f/f 2 <0.2 Condition (1)
−0.2 <f/f 4 <0.2 Condition (2)
f 1 /f 3 >2 Condition (3)
where
f is the focal length of the single focus lens,
f 1 is the focal length of the first lens element, in order from the object side,
f 2 is the focal length of the second lens element, in order from the object side,
f 3 is the focal length of the third lens element, in order from the object side, and
f 4 is the focal length of the fourth lens element, in order from the object side.
8. The single focus lens according to claim 4 , wherein the following Conditions (1), (2) and (3) are satisfied:
−0.2 <f/f 2 <0.2 Condition (1)
−0.2 <f/f 4 <0.2 Condition (2)
f 1 /f 3 >2 Condition (3)
where
f is the focal length of the single focus lens,
f 1 is the focal length of the first lens element, in order from the object side,
f 2 is the focal length of the second lens element, in order from the object side,
f 3 is the focal length of the third lens element, in order from the object side, and
f 4 is the focal length of the fourth lens element, in order from the object side.
9. The single focus lens according to claim 1 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
10. The single focus lens according to claim 2 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
11. The single focus lens according to claim 3 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
12. The single focus lens according to claim 4 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
13. The single focus lens according to claim 5 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
14. The single focus lens according to claim 6 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
15. The single focus lens according to claim 7 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.
16. The single focus lens according to claim 8 , wherein the following Conditions (4), (5) and (6) are satisfied:
N d1 >1.70 Condition (4)
υ d1 <35 Condition (5)
υ d3 >50 Condition (6)
where
N d1 is the index of refraction at the d-line of the first lens element, in order from the object side,
υ d1 is the Abbe number at the d-line of the first lens element, in order from the object side, and
υ d3 is the Abbe number at the d-line of the third lens element, in order from the object side.