Miniature telephoto lens assembly
An optical lens assembly includes five lens elements and provides a TTL/EFL<1.0. In an embodiment, the focal length of the first lens element f1<TTL/2, an air gap between first and second lens elements is smaller than half the second lens element thickness, an air gap between the third and fourth lens elements is greater than TTL/5 and an air gap between the fourth and fifth lens elements is smaller than about 1.5 times the fifth lens element thickness. All lens elements may be aspheric.
1. A lens assembly, comprising: a plurality of refractive lens elements arranged along an optical axis, wherein at least one surface of at least one of the plurality of lens elements is aspheric, wherein the lens assembly has an effective focal length (EFL), wherein a lens system that includes the lens assembly plus a window positioned between the plurality of lens elements and an image plane has a total track length (TTL) of 6.5 millimeters or less, wherein a ratio TTL/EFL is less than 1.0, wherein the plurality of lens elements comprises, in order from an object side to an image side, a first lens element with positive refractive power, a second lens element with negative refractive power, and a third lens element, wherein a focal length f1 of the first lens element is smaller than TTL/2 and wherein a lens assembly F # is smaller than 2.9.
2. The lens assembly of claim 1 , wherein the third lens element has negative refractive power.
3. The lens assembly of claim 1 , wherein the plurality of refractive lens elements includes five lens elements.
4. The lens assembly of claim 1 , wherein the focal length f1, a focal length f2 of the second lens element and a focal length f3 of the third lens element fulfill the condition 1.2×|f3|>|f2|>1.5×f1.
5. The lens assembly of claim 2 , wherein the plurality of refractive lens elements includes five lens elements, and wherein a fourth lens element and a fifth lens element have different refractive power signs.
6. The lens assembly of claim 3 , wherein a fourth lens element and a fifth lens element have different refractive power signs.
7. The lens assembly of claim 3 , wherein a fourth lens element and a fifth lens element are separated by an air gap smaller than TTL/20.
8. The lens assembly of claim 3 , wherein one of a fourth lens element and a fifth lens element is characterized by an Abbe number smaller than 30 and wherein the other of the fourth lens element and the fifth lens element is characterized by an Abbe number greater than 50.
9. The lens assembly of claim 5 , wherein the third lens element and the fourth lens element are separated by an air gap greater than TTL/5, wherein the fourth lens element and the fifth lens element are separated by an air gap smaller than TTL/20, wherein one of the fourth lens element and the fifth lens element is characterized by an Abbe number smaller than 30, and wherein the other of the fourth lens element and the fifth lens element is characterized by an Abbe number greater than 50.
10. The lens assembly of claim 6 , wherein the third lens element and the fourth lens element are separated by an air gap greater than TTL/5, wherein the fourth lens element and the fifth lens element are separated by an air gap smaller than TTL/20, wherein one of the fourth lens element and the fifth lens element is characterized by an Abbe number smaller than 30, and wherein the other of the fourth lens element and the fifth lens element is characterized by an Abbe number greater than 50.
11. A lens assembly, comprising: a plurality of refractive lens elements arranged along an optical axis, wherein at least one surface of at least one of the plurality of lens elements is aspheric, wherein the lens assembly has an effective focal length (EFL), wherein a lens system that includes the lens assembly plus a window positioned between the plurality of lens elements and an image plane has a total track length (TTL) of 6.5 millimeters or less, wherein a ratio TTL/EFL is less than 1.0, wherein the plurality of lens elements comprises, in order from an object side to an image side, a first lens element with positive refractive power and a focal length f1, a second lens element with negative refractive power and a focal length f2, and a third lens element with a focal length f3, wherein the focal length f1, the focal length f2 and the focal length f3 fulfill the condition 1.2×|f3|>|f2|>1.5×f1, and wherein a lens assembly F # is smaller than 2.9.
12. The lens assembly of claim 11 , wherein the third lens element has negative refractive power.
13. The lens assembly of claim 11 , wherein the plurality of refractive lens elements includes five lens elements.
14. The lens assembly of claim 12 , wherein the plurality of refractive lens elements includes five lens elements, and wherein a fourth lens element and a fifth lens element have different refractive power signs.
15. The lens assembly of claim 13 , wherein a fourth lens element and a fifth lens element have different refractive power signs.
16. The lens assembly of claim 13 , wherein a fourth lens element and a fifth lens element are separated by an air gap smaller than TTL/20.
17. The lens assembly of claim 13 , wherein one of a fourth lens element and a fifth lens element is characterized by an Abbe number smaller than 30 and wherein the other of the fourth lens element and the fifth lens element is characterized by an Abbe number greater than 50.
18. A lens assembly, comprising: five refractive lens elements arranged along an optical axis, wherein at least one surface of at least one of the lens elements is aspheric wherein the lens assembly has an effective focal length (EFL), a total track length (TTL) of 6.5 millimeters or less and a ratio TTL/EFL of less than 1.0, wherein the lens elements comprises, in order from an object side to an image side, a first lens element with positive refractive power, a second lens element with negative refractive power, a third lens element and a fourth lens element, wherein the third lens element and the fourth lens element are separated by an air gap greater than TTL/5 and wherein a lens assembly F # is smaller than 2.9.
19. The lens assembly of claim 18 , wherein the third lens element has negative refractive power.
20. The lens assembly of claim 18 , wherein the fourth lens element and a fifth lens element have different refractive power signs.
21. The lens assembly of claim 18 , wherein the fourth lens element and the fifth lens element are separated by an air gap smaller than TTL/20.
22. The lens assembly of claim 18 , wherein one of the fourth lens element and a fifth lens element is characterized by an Abbe number smaller than 30 and wherein the other of the fourth lens element and the fifth lens element is characterized by an Abbe number greater than 50.
23. The lens assembly of claim 18 , wherein a focal length f1 of the first lens element is smaller than TTL/2.
24. The lens assembly of claim 19 , wherein the fourth lens element and a fifth lens element have different refractive power signs.