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 which are spaced apart by 0.5 mm,
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 a fixed ratio of total track length of the optical assembly to effective focal length (hereinafter “TTL/EFL”) is less than 12.
2 . The optical assembly of claim 1 , wherein the total track length TTL is less than 10 cm.
3 . The optical assembly of claim 1 , wherein said TTL/EFL ratio is less than 8.
4 . The optical assembly of claim 1 , comprising a fourth optical group configured to deliver a telecentric cone to an image sensor.
5 . The optical assembly of claim 4 , wherein the fourth optical group comprises a convexo-planar, convexo-quasi-planar or convexo-concave lens element.
6 . The optical assembly of claim 5 , wherein the fourth optical group further comprises a second convexo-planar, convexo-quasi planar or convexo-concave lens element.
7 . The optical assembly of claim 1 , wherein said optical assembly has a maximum lateral chromatic aberration of less than 5 microns.
8 . The optical assembly of claim 1 , wherein said first optical group comprises a convexo-concave or meniscus lens.
9 . The optical assembly of claim 8 , wherein said first optical group further comprises a biconcave lens.
10 . The optical assembly of claim 8 , wherein a diameter of said convexo-concave or meniscus lens of said first optical group is less than 30 mm.
11 . The optical assembly of claim 8 , wherein the ratio of diameter of said convexo-concave or meniscus lens of said first optical group to image size is less than 3.
12 . The optical assembly of claim 1 , wherein the optical assembly has an axial chromatic aberration that is less than 0.025 microns.
13 . The optical assembly of claim 12 , wherein the axial chromatic aberration is defined across a spectral band between 465 nm to 650 nm.
14 . 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.
15 . The digital camera of claim 14 , wherein a stray light irradiance ratio is below 1/10,000.
16 . The digital camera of claim 14 , wherein a stray light power ratio is below 1/100.
17 . 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 aspheric surface comprises a maximum aspheric sag across said aspheric surface that is less than approximately 10 microns.
18 . The optical assembly of claim 17 , wherein said aspheric surface comprises a maximum aspheric sag slope across said aspheric surface that is less than approximately 15 microns per millimeter.
19 . A digital point action camera, comprising
an optical assembly as in claim 17 ; 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.
20 . 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 aspheric surface comprises a maximum aspheric sag slope across said aspheric surface that is less than approximately 15 microns per millimeter.
21 . A digital point action camera, comprising
an optical assembly as in claim 20 ; 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.