Lens system
Compact narrow angle lens systems that may be used in small form factor cameras. The lens system may include six lens elements with refractive power, and may provide lower F-numbers while maintaining or improving imaging quality and package size when compared to other compact lens systems. Total track length of the lens system may be 6.5 millimeters or less, for example 5.9 or 6 millimeters. Focal length of the lens system may be 7.0 millimeters or less, for example 6.6 millimeters. The lens system may include an aperture stop located behind the front vertex of the lens system, for example between the first and second lens elements, that effectively moves the ideal principal point of the camera to in front of the front vertex. The lens system may provide a focal ratio of 2.8 or less, for example 2.6 or 2.4.
1. A lens system, comprising:
a plurality of refractive lens elements arranged along an optical axis of the lens system, wherein the plurality of lens elements includes, in order along the optical axis from an object side to an image side:
a first lens element with positive refractive power having a convex object side surface;
a second lens element with negative refractive power having a concave image side surface;
a third lens element;
a fourth lens element with negative refractive power;
a fifth lens element; and
a sixth lens element with positive refractive power having a convex image side surface;
wherein the lens system has effective focal length f within a range of 6.0 to 7.0 millimeters, and wherein total track length (TTL) of the lens system is within a range of 5.5 to 6.5 millimeters.
2. The lens system as recited in claim 1 , wherein focal ratio of the lens system is 2.8 or less.
3. The lens system as recited in claim 1 , wherein the third lens element from the object side of the lens system is a positive lens with positive refractive power, and wherein the fifth lens element from the object side of the lens system is a negative lens with negative refractive power.
4. The lens system as recited in claim 1 , wherein the lens system further comprises an aperture stop located at the first lens element from the object side of the lens system and behind a front vertex of the lens system.
5. The lens system as recited in claim 4 , wherein effective aperture of the lens system is 2.6 millimeters or less.
6. The lens system as recited in claim 1 , wherein the lens system further comprises an aperture stop located between the first lens element and the second lens element of the lens system.
7. The lens system as recited in claim 6 , wherein effective aperture of the lens system is 2.8 millimeters or less.
8. The lens system as recited in claim 1 , wherein telephoto ratio (TTL/f) of the lens system is less than or equal to 1.0.
9. A lens system, comprising:
six refractive lens elements arranged along an optical axis and configured to refract light from an object field to form an image of a scene at an image plane; and
an aperture stop located behind a front vertex of the lens system;
wherein the lens system has effective focal length f within a range of 6.0 to 7.0 millimeters, wherein total track length (TTL) of the lens system is within a range of 5.5 millimeters to 6.5 millimeters, and wherein focal ratio of the lens system is 2.8 or less; and
wherein locating the aperture stop behind the front vertex acts to move an ideal principal point of the lens system forward in front of the front vertex of the lens system.
10. The lens system as recited in claim 9 , wherein the lens elements include, in order along the optical axis from an object side to an image side:
a first lens element with positive refractive power having a convex object side surface;
a second lens element with negative refractive power having a concave image side surface;
a third lens element;
a fourth lens element with negative refractive power;
a fifth lens element; and
a sixth lens element with positive refractive power having a convex image side surface.
11. The lens system as recited in claim 10 , wherein the third lens element from the object side of the lens system is a positive lens with low positive refractive power.
12. The lens system as recited in claim 10 , wherein the fifth lens element from the object side of the lens system is a negative lens with negative refractive power.
13. The lens system as recited in claim 10 , wherein the second lens element has a concave object side surface, wherein the third lens element has a convex image side surface, and wherein the fourth lens element has a concave image side surface.
14. The lens system as recited in claim 9 , wherein effective aperture of the lens system is 2.8 millimeters or less.
15. The lens system as recited in claim 9 , wherein at least one surface of at least one of the six refractive lens elements is aspheric.
16. The lens system as recited in claim 9 , wherein at least one of the six refractive lens elements is composed of a first plastic material, and wherein at least one other of the six refractive lens elements is composed of a second plastic material with different optical characteristics than the first plastic material.
17. The lens system as recited in claim 9 , wherein the lens system has effective focal length f, and wherein telephoto ratio (TTL/f) of the lens system is less than or equal to 1.0.
18. A device, comprising:
one or more processors;
one or more cameras; and
a memory comprising program instructions executable by at least one of the one or more processors to control operations of the one or more cameras;
wherein at least one of the one or more cameras is a narrow angle camera comprising:
a photosensor configured to capture light projected onto a surface of the photosensor; and
a lens system configured to refract light from an object field located in front of the camera to form an image of a scene at an image plane proximate to the surface of the photosensor, wherein the lens system comprises six refractive lens elements arranged along an optical axis of the camera; and
wherein the lens system has effective focal length f within a range of 6.0 to 7.0 millimeters, wherein total track length (TTL) of the lens system is within a range of 5.5 millimeters to 6.5 millimeters, and wherein focal ratio of the lens system is 2.8 or less.
19. The device as recited in claim 18 , wherein the lens system further comprises an aperture stop located behind a front vertex of the lens system, wherein locating the aperture stop behind the front vertex acts to move an ideal principal point of the camera forward in front of the front vertex of the lens system.