Optical assembly for a compact wide field of view digital camera with low first lens diameter to image diagonal ratio

1. An optical assembly for a point action camera having a wide field of view, comprising from object end to image end:

a first optical group including two or more lens elements configured to collect and reduce a field angle of light incident at a field of view in excess of 120 degrees;

a second optical group including a doublet;

a third optical group including two or more lens elements, wherein at least one lens element of the third optical group

includes an aspheric surface that is configured to correct higher order astigmatism; and

a fourth optical group configured to deliver a telecentric cone to the image sensor; and

wherein the optical assembly further comprises an aperture stop between said second and third optical groups, and

wherein a ratio of a diameter of a first lens element at the object end of the optical assembly to an image diagonal is less than approximately 3, and

wherein the optical assembly comprises a depth of focus that is greater than 20 microns.

2. The optical assembly of claim 1 , wherein said depth of focus is determined as a full width at half maximum of a distribution of diffraction modulation transfer function (“diffraction MTF”) versus defocusing position across said field of view in excess of 120 degrees.

3. The optical assembly of claim 1 , wherein a diameter of a convexo-concave or meniscus lens of said first optical group is less than 30 mm.

4. The optical assembly of claim 1 , wherein a diameter of a convexo-concave or meniscus lens of said first optical group is less than 25 mm.

5. The optical assembly of claim 1 , comprising less than five microns of lateral chromatic aberration.

6. The optical assembly of claim 1 , comprising a ratio of total track length to effective focal length of the optical assembly (hereinafter “TTL/EFL”) that is less than 10.

7. The optical assembly of claim 6 , wherein the total track length TTL is less than 8 cm.

8. The optical assembly of claim 1 , wherein said TTL/EFL ratio is less than 8 .

9. The optical assembly of claim 1 , wherein the fourth optical group comprises two spaced apart lens elements.

10. The optical assembly of claim 9 , wherein the fourth optical group comprises a convexo-planar, convexo-quasi-planar or convexo-concave lens element.

11. The optical assembly of claim 10 , wherein the fourth optical group further comprises a second convexo-planar, convexo-quasi planar or convexo-concave lens element.

12. The optical assembly of claim 1 , wherein said first optical group comprises a convexo-concave or meniscus lens.

13. The optical assembly of claim 12 , wherein said first optical group further comprises a doublet.

14. The optical assembly of claim 13 , wherein said doublet of said first optical group comprises a biconcave lens coupled to a biconvex lens.

15. The optical assembly of claim 12 , wherein the first optical group further comprises a second convexo-concave or meniscus lens.

16. The optical assembly of claim 15 , wherein said first optical group further comprises a doublet.

17. The optical assembly of claim 1 , wherein the third optical group further comprises a doublet.

18. The optical assembly of claim 17 , wherein said doublet of said third optical group comprises a biconcave lens coupled to a biconvex lens.

19. The optical assembly of claim 1 , wherein said doublet of said second optical group comprises a convexo-concave lens coupled to a biconvex, convexo-quasi-convex or convexo-planar lens.

20. The optical assembly of claim 1 , wherein axial chromatic aberration is less than 0.025 microns.

21. The optical assembly of claim 20 , wherein the axial chromatic aberration is defined across a spectral band between 465 nm to 650 nm.