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 system, comprising:
a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of refractive lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL;
a window positioned between the plurality of lens elements and an image plane, wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 2.9, and a ratio L11/L1e between a largest optical axis thickness L11 and a circumferential edge thickness L1e of the first lens element smaller than 3.08; and
a stop positioned before the first lens element, wherein the plurality of lens elements includes, in order from an object side to an image sidee, a first group comprising the first lens element, a second lens element with negative refractive power and a third lens element, and a second group comprising a first element of the second group and a second lens element of the second group, wherein the first and second groups are separated by a gap that is larger than twice any other gap between lens elements, wherein the first lens element has positive refractive power and wherein the first element of the second group and the second lens element of the second group have opposite refractive powers.
2. The lens system of claim 1 , wherein the ratio L11/L1e smaller than 3.2.
3. The lens system of claim 1 , wherein the ratio L11/L1e smaller than 3.1.
4. The lens system of claim 1 , wherein the ratio L11/L1e smaller than 3.0.
5. The lens system of claim 1 , wherein the TTL of 6.0 mm or less.
6. A lens system, comprising:
a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of refractive lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL;
a window positioned between the plurality of lens elements and an image plane, wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 2.9, and a ratio L11/L1e between a largest optical axis thickness L11 and a circumferential edge thickness L1e of the first lens element smaller than 3.08; and
a stop positioned before the first lens element,
wherein the plurality of lens elements includes, in order from an object sside to an image side, a first group comprising the first lens element, a second lens element with a focal length f2 and a third lens element with a focal length f3, and a second group comprising a first element of the second group and a second lens element of the second group, wherein the first element has a focal length f1 and a positive refractive power, wherein the second lens element has a negative refractive power, wherein 1.2×|f3|>f2|>1.5×f1 and wherein the first element of the second group and the second lens element of the second group have opposite refractive powers.
7. A lens system, comprising:
a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of refractive lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL;
a window positioned between the plurality of lens elements and an image plane, wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 2.9, and a ratio L11/L1e between a largest optical axis thickness L11 and a circumferential edge thickness L1e of the first lens element smaller than 3.08; and
a stop positioned before the first lens element,
wherein the plurality of lens elements comprises, in order from an object side to an image side, a first lens element with a focal length f1 and positive refractive power, a second lens element with a focal length f2 and negative refractive power and a third lens element with a focal length f3, the focal length f1, the focal length f2 and the focal length f3 fulfilling a condition 1.2×|f3|>|f2|>1.5×f1, wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm, wherein the F number is smaller than 2.9 and wherein the plurality of lens elements further comprises a fourth lens element, the third and fourth lens elements being separated by an air gap greater than TTL/5.
8. A lens system, comprising:
a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of refractive lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL;
a window positioned between the plurality of lens elements and an image plane, wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 2.9, and a ratio L11/L1e between a largest optical axis thickness L11 and a circumferential edge thickness L1e of the first lens element smaller than 3.08; and
a stop positioned before the first lens element,
wherein the plurality of refractive lens elements comprises, in order from an object plane to an image plane along the optical axis, a first lens element having positive optical power, a pair of second and third lens elements having together a negative optical power, and a combination of fourth and fifth lens elements, the fourth lens element separated from the third lens element by an air gap greater than TTL/5, and wherein a center thickness along the optical axis of each one of the plurality of lens elements is at least 0.2 mm.
9. The lens system of claim 1 , wherein f1<TTL/2.
10. The lens system of claim 1 , wherein 1.2×|f3|>|f2|>1.5×f1.
11. The lens system of claim 1 , wherein a combined power of the second and third lens elements is negative.
12. The lens system of claim 1 , wherein the third lens element has negative refractive power.
13. The lens system of claim 1 , wherein the first element of the second group and the second lens element of the second group are separated by a gap smaller than 1.5×d5, where d5 is a thickness of the fifth lens element along the optical axis.
14. The lens system of claim 1 , wherein the first element of the second group and the second lens element of the second group are separated by a gap smaller than TTL/20.
15. The lens system of claim 1 , wherein the first element of the second group and the second lens element of the second group are made of different lens materials having different Abbe numbers, such that one lens element has Abbe number that is smaller than 30 and the other lens element has an Abbe number that is larger than 50.
16. A lens system, comprising:
a lens assembly comprising a plurality of refractive lens elements arranged along an optical axis with a first lens element on an object side, wherein at least one surface of at least one of the plurality of lens elements is aspheric, and wherein the lens assembly has an effective focal length EFL; and
a window positioned between the plurality of lens elements and an image plane,
wherein the lens system has a total track length TTL of 6.5 mm or less, a ratio TTL/EFL smaller than 1.0, a F number smaller than 3.2, and a ratio L11/L1e between a largest optical axis thickness L11 and a circumferential edge thickness L1e of the first lens element smaller than 3.08,
wherein the plurality of lens elements includes, in order from an object side to an image side, a first group comprising the first lens element, a second lens element with negative refractive power and a third lens element, and a second group comprising a first element of the second group and a second lens element of the second group,
wherein the first and second groups are separated by a gap that is larger than twice any other gap between lens elements,
wherein the first lens element has positive refractive power and wherein the first element of the second group and the second lens element of the second group have opposite refractive powers, and
wherein the first element of the second group and the second lens element of the second group are made of different lens materials having different Abbe numbers, such that one lens element has Abbe number that is smaller than 30 and the other lens element has an Abbe number that is larger than 50.