Optical assembly for a compact wide field of view digital camera with high MTF
An optical assembly for a point action camera or other compact digital camera having a wide field of view, includes multiple lens elements, including at least one lens element that has an aspheric lens surface. The optical assembly is configured to provide a field of view in excess of 120 degrees. The optical assembly has a modulation transfer function (hereinafter “MTF”) at the Nyquist frequency that is above 0.3 and a MTF at half Nyquist frequency that is above 0.5 across the wide field of view.
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 two or more spaced apart lens elements,
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
an aperture stop between said second and third optical groups;
wherein said optical assembly comprises a modulation transfer function (hereinafter “MTF”) at Nyquist frequency approximately 200 line pairs per millimeter that is above 0.3 and a MTF at half Nyquist frequency approximately 100 line pairs per millimeter that is above 0.5 across said wide field of view.
2. The optical assembly of claim 1 , comprising a MTF at Nyquist frequency above 0.35 and a MTF at half Nyquist frequency above 0.55.
3. The optical assembly of claim 1 , comprising a ratio of total track length of the optical assembly to an effective focal length of the optical assembly (hereinafter “TTL/EFL”) that is less than 12.
4. The optical assembly of claim 3 , wherein the total track length TTL is less than 10 cm.
5. The optical assembly of claim 3 , wherein said TTL/EFL ratio is less than 8.
6. The optical assembly of claim 1 , comprising a fourth optical group configured to deliver a telecentric cone to the image sensor.
7. The optical assembly of claim 6 , wherein the fourth optical group comprises a convexo-planar, convexo-quasi-planar or convexo-concave lens element.
8. The optical assembly of claim 7 , wherein the fourth optical group further comprises a second convexo-planar, convexo-quasi planar or convexo-concave lens element.
9. The optical assembly of claim 1 , wherein said optical assembly has a lateral chromatic aberration of less than 5 microns.
10. The optical assembly of claim 1 , wherein said first optical group comprises a convexo-concave or meniscus lens.
11. The optical assembly of claim 10 , wherein said first optical group further comprises a biconcave lens.
12. The optical assembly of claim 10 , wherein a diameter of said convexo-concave or meniscus lens of said first optical group is less than 30 mm.
13. The optical assembly of claim 10 , wherein the ratio of diameter of said convexo-concave or meniscus lens of said first optical group to image size is less than 3.
14. The optical assembly of claim 1 , wherein the second optical group comprises a doublet.
15. The optical assembly of claim 1 , wherein the third optical group comprises a doublet.
16. The optical assembly of claim 1 , wherein at least one aspheric surface comprises an aspheric sag less than approximately 10 microns.
17. The optical assembly of claim 1 , wherein at least one aspheric surface comprises an aspheric sag slope less than approximately 15 microns per millimeter.
18. The optical assembly of claim 1 , comprising a single aspheric lens element, which is the only aspheric lens element within the optical assembly, wherein lens elements other than the single aspheric lens element comprise spherical or planar lens surfaces, or both, each without significant aspheric departure.
19. The optical assembly of claim 1 , comprising a single aspheric lens surface, which is the only aspheric lens surface within the optical assembly, wherein lens surfaces other than said aspheric lens surface comprise spherical or planar lens surfaces, or both, each without significant aspheric departure.
20. The optical assembly of claim 1 , comprising only one aspheric lens element.
21. The optical assembly of claim 1 , comprising only one aspheric lens surface.
22. The optical assembly of claim 1 , wherein axial chromatic aberration is less than 0.025 microns.
23. The optical assembly of claim 22 , wherein the axial chromatic aberration is defined across a spectral band between 465 nm to 650 nm.
24. A digital point action camera, comprising
an optical assembly as in claim 1 ; and
an image sensor disposed approximately at a focal plane of the optical assembly; and
a digital camera housing including electronics and a user interface, and containing said optical assembly and said image sensor in optically effective relative disposition.
25. The digital camera of claim 24 , wherein 90% or more of return ghost foci are displaced at least 2 mm from the image sensor.
26. The digital camera of claim 24 , wherein a stray light irradiance ratio is below 1/10,000.
27. The digital camera of claim 24 , wherein a stray light power ratio is below 1/100.