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EP-4737972-A2 - FOLDED LENS SYSTEM WITH FOUR REFRACTIVE LENSES

EP4737972A2EP 4737972 A2EP4737972 A2EP 4737972A2EP-4737972-A2

Abstract

Compact folded lens systems are described that may be used in small form factor cameras. Lens systems are described that may include four lens elements with refractive power, with a light folding element such as a prism, located between a first lens element on the object side of the lens system and a second lens element, that redirects the light refracted from the first lens element from a first axis onto a second axis on which the other lens elements and a photosensor are arranged. The lens systems may include an aperture stop located behind the front vertex of the lens system, for example at the first lens element, and an optional infrared filter, for example located between the last lens element and a photosensor.

Inventors

  • YAO, YUHONG
  • SHINOHARA, YOSHIKAZU

Assignees

  • Apple Inc.

Dates

Publication Date
20260506
Application Date
20170328

Claims (15)

  1. A lens system, comprising: a folded 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 at or near the surface of the photosensor, wherein the lens system comprises four refractive lens elements arranged along a folded optical axis of the camera from an object side to an image side and a light folding element located between a first and second lens element from the object side and configured to redirect light from a first axis onto a second axis; wherein the lens system provides a 35 mm equivalent focal length in the range of 55 - 140 mm and less than 6.5 mm of Z-height measured from a front vertex of the lens system to a rear vertex of the light folding element.
  2. The lens system as recited in claim 1, wherein the first lens element has positive refractive power, and the second lens element has negative refractive power.
  3. The lens system as recited in claim 1 or claim 2, wherein the lens system further comprises an aperture stop located between the object side of the lens system and the light folding element.
  4. The lens system as recited in any one of claims 1-3, wherein the lens system provides a 35 mm equivalent focal length in the range of 75 - 120 mm and less than 6 mm of Z-height measured from the front vertex of the lens system to the rear vertex of the folding element.
  5. The lens system as recited in any one of claims 1-4, wherein the first lens element has positive refractive power and is the only lens element on the object side of the light folding element.
  6. The lens system as recited in any one of claims 1-5, wherein the first lens element and a fourth lens element are formed of optical materials with Abbe number Vd > 40, and the second lens element is formed of an optical material with Abbe number Vd < 30.
  7. The lens system as recited in any one of claims 1-6, wherein the lens system satisfies one or more of the relationships: 0.4 < f / f 1 < 1 0.8 < f / f 2 < 1.6 0.05 < R 4 f − R 4 r / R 4 f + R 4 r < 0.8 where f is effective focal length of the lens system, fl is focal length of the first lens element, f2 is focal length of the second lens element, R4f is radius of curvature of the object-side surface of a fourth lens element, and R4r is radius of curvature of the image side surface of the fourth lens element.
  8. The lens system as recited in any one of claims 1-7, wherein the light folding element is a prism and an image side surface of the first lens element is flat/plano, and wherein the image side surface of the first lens element is in contact with the object side surface of the prism.
  9. The lens system as recited in any one of claims 1-8, wherein effective focal length of the lens system is within a range of 6.5 millimeters to 14 millimeters.
  10. The lens system as recited in any one of claims 1-9, wherein focal ratio (F/#) of the lens system is within a range of 2.2 to 3.
  11. The lens system as recited in any one of claims 1-10, wherein full field of view (FOV) of the lens system is within a range of 20.4° to 42.2°.
  12. A camera, comprising: a photosensor configured to capture light projected onto a surface of the photosensor; and a folded lens system as recited in any one of claim 1-11.
  13. The camera as recited in claim 12, wherein effective focal length of the lens system is within a range of 6.5 millimeters to 14 millimeters, and wherein the photosensor is between 4 millimeters and 8 millimeters in a diagonal dimension.
  14. The camera as recited in claim 12 or claim 13, wherein the photosensor is configured to move on one or more axes relative to the lens system to adjust focus of the camera.
  15. A device, comprising: one or more processors; a camera as recited in any one of claims 12-14; and a memory comprising program instructions executable by at least one of the one or more processors to control operations of the camera.

Description

BACKGROUND Technical Field This disclosure relates generally to camera systems, and more specifically to compact lens systems for high-resolution, small form factor camera systems. Description of the Related Art The advent of small, mobile multipurpose devices such as smartphones and tablet or pad devices has resulted in a need for high-resolution, small form factor cameras for integration in the devices. However, due to limitations of conventional camera technology, conventional small cameras used in such devices tend to capture images at lower resolutions and/or with lower image quality than can be achieved with larger, higher quality cameras. Achieving higher resolution with small package size cameras generally requires use of a photosensor (also referred to as an image sensor) with small pixel size and a good, compact imaging lens system. Advances in technology have achieved reduction of the pixel size in photosensors. However, as photosensors become more compact and powerful, demand for compact imaging lens system with improved imaging quality performance has increased. SUMMARY OF EMBODIMENTS Compact folded lens systems are described that may be used in small form factor cameras. Lens systems are described that may include four lens elements with refractive power, with a light folding element such as a prism located between a first lens element on the object side of the lens system and a second lens element that redirects the light refracted from the first lens element from a first axis onto a second axis on which the other lens elements and a photosensor are arranged. The lens systems may include an aperture stop located behind the front vertex of the lens system, for example at the first lens element, and an optional infrared filter, for example located between the last lens element and a photosensor of the camera. Embodiments of the compact folded lens system may include four lens elements with refractive power and a light folding element such as a prism to fold the optical axis. The compact folded lens system may be configured to operate with a relatively narrow field of view and a 35 mm equivalent focal length (f35mm) in the telephoto range. For example, some embodiments of the compact folded lens system may provide a 35 mm equivalent focal length in the range of 55 - 140 mm, with less than 6.5 mm of Z-height to fit in a wide variety of portable electronics devices. Through proper arrangement in materials, power and radius of curvature of the four lens elements with power, embodiments of the compact folded lens are capable of capturing high resolution, high quality images at good brightness level. In some embodiments, a first lens element from the object side of the lens system has a convex object-side surface in the paraxial region, and a third lens element has a concave image-side surface in the paraxial region. In some embodiments, a first lens element from the object side of the lens system has a convex object-side surface in the paraxial region, and a third lens element has a concave image-side surface in the paraxial region. In some embodiments, the first lens elements is formed of optical materials with Abbe number Vd > 40, and the second lens element is formed of an optical material with Abbe number Vd < 30. In some embodiments, the first and fourth lens elements are formed of optical materials with Abbe number Vd > 40, and the second lens element is formed of an optical material with Abbe number Vd < 30. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional illustration of a compact camera including an example embodiment of a compact folded lens system with four lens elements and a light folding element.FIGS. 2A and 2B show a camera that includes an example embodiment of a compact folded lens system that operates at F/2.4, with 31° full field of view (FOV).FIG. 3 shows a camera that includes an example embodiment of a compact folded lens system that operates at F/2.4, with 28.1° full FOV.FIG. 4 shows a camera that includes an example embodiment of a compact folded lens system that operates at F/2.2, with 42.2° full FOV.FIG. 5 shows a camera that includes an example embodiment of a compact folded lens system that operates at F/2.6, with 23.7° full FOV.FIG. 6 shows a camera that includes an example embodiment of a compact folded lens system that operates at F/2.4, with 31.2° full FOV.FIG. 7 shows a camera that includes an example embodiment of a compact folded lens system that operates at F/3, with 20.4° full FOV.FIG. 8 illustrates numbering of the surfaces in the example lens systems as used in the Tables.FIG. 9 is a flowchart of a method for capturing images using cameras with lens systems as illustrated FIGS. 1 through 7, according to some embodiments.FIG. 10 illustrates an example computer system that may be used in embodiments. This specification includes references to "one embodiment" or "an embodiment." The appearances of the phrases "in one embodiment" or "in an embodiment"