Lens system for a camera module
View Patent ↗An optical system for a shallow form factor camera module comprises: seven even aspheric singlet lens elements formed of a molded plastics material, a flat image sensor, and a central aperture stop with at least 3 lens elements disposed in front of the aperture stop and at least 3 rear lens elements disposed between the aperture stop and the image sensor. The aperture stop has a pupil wide enough to provide at least f/1.0 aperture and the optical system has a total track length less than about 8.2 mm and a minimum spacing of about 0.6 mm between a surface of the rearmost lens element and an imaging plane of said image sensor. A magnitude of an aspheric coefficient for h 4 of at least one surface of each of said rear lens elements is greater than 5×10 −2 .
1. A camera module for a shallow form factor device, the camera module comprising an optical system comprising:
seven even aspheric singlet lens elements formed of a molded plastics material, a flat image sensor, and
a central aperture stop with at least 3 lens elements disposed in front of said aperture stop and at least 3 rear lens elements disposed between said aperture stop and said image sensor, said aperture stop having a pupil wide enough to provide an aperture having an f-number of at least f/1.0,
wherein said optical system has a total track length (TTL) less than about 8.2 mm and a minimum spacing of about 0.6 mm between a surface of the rearmost lens element and an imaging plane of said image sensor where sag z at height h for a surface of each lens element is described by the formula:
z=f ( h 2 ,R,k )+ A 1 h 4 +A 2 h 6 +A 3 h 8 +A 4 h 10 +A 5 h 12 +A 6 h 14 ,
where R is radius of curvature;
k is conic constant; and
A 1 to A 6 are aspheric coefficients, where a magnitude of an aspheric coefficient A 1 of at least one surface of each of said rear lens elements is greater than 5×10 −2 .
2. The camera module according to claim 1 wherein said optical system has a back-focal length about 0.82 mm from the centre of the lens.
3. The camera module according to claim 1 wherein said optical system has a target focal length of about 5 mm.
4. The camera module according to claim 1 wherein the plastics materials for said lens elements have a refractive index of n=1.53 and an Abbe number V=56; or a refractive index n=1.63 and an Abbe number V=24 at 25° C.
5. The camera module according to claim 1 wherein said image sensor has an area of 4.8 mm×3.6 mm.
6. The camera module according to claim 1 comprising 4 rear lens elements and wherein from front to rear:
a first and second of said lens elements have a positive optical power,
a third lens element is configured to reduce a spherical aberration and coma introduced by the first two lens elements,
a fourth and fifth of said lens elements correct for distortion, and
a sixth and seventh of said lens elements act as field flatteners.
7. The camera module according to claim 1 wherein:
f
(
h
2
,
R
,
k
)
=
h
2
R
+
R
2
-
(
k
+
1
)
R
2
.
8. A smartphone incorporating the camera module of claim 1 and further comprising a processor operatively coupled to said image sensor and being arranged to read image data from said image sensor and to write said image data to a memory.