Optical arrangement for wide angle imaging lens with front entrance pupil
A method and apparatus for capturing an image of at least one object appearing in a wide-angle field of view (FOV). A housing has an image sensor and a lens assembly fixedly mounted relative thereto. The lens assembly includes first and second lens groups, and a glass lens. The lens assembly and the image sensor are aligned such that light received within the FOV passes through a front aperture and the base lens assembly and impinges onto the image sensor. The light received from the FOV forms an original image prior to entering the front aperture and the lens assembly. Light from the FOV impinging onto the sensor forms an impinging image.
1. An optical assembly for wide angle imaging of an object of interest, the optical assembly comprising:
a front aperture disposed along an optical axis configured to receive light from the object of interest therethrough along the optical axis;
a first lens group disposed along the optical axis relative to the front aperture to receive the light from the object of interest through the front aperture and configured to correct for spherical aberrations of an image projected by a second lens group onto an imaging sensor;
a glass lens disposed along the optical axis configured to receive the light from the first lens group, the glass lens having a first flat surface and a second spherical surface opposite the first flat surface disposed along the optical axis, the glass lens being a Crown type glass having a positive optical power;
the second lens group disposed along the optical axis configured to receive the light from the glass lens and further configured to correct for optical field distortions and aberrations of the image projected by the second lens group; and
the imaging sensor being disposed along the optical axis at a back focal distance of the second lens group, and configured to receive the image from the second lens group and to generate an electrical signal indicative of the image, wherein the back focal distance is equal to or greater than 0.5 millimeters in proximity to the imaging sensor,
wherein the first lens group comprises a first plastic aspheric lens and a second plastic aspheric lens, the first plastic aspheric lens of the first lens group disposed along the optical axis between the second plastic aspheric lens and the aperture, and
wherein the second lens group comprises a first plastic aspheric lens and a second plastic aspheric lens, the first plastic aspheric lens of the second lens group is disposed along the optical axis between the second plastic aspheric lens and the glass lens.
2. The optical assembly of claim 1 , wherein the imaging sensor is a solid-state imager.
3. The optical assembly of claim 1 , wherein the second lens group configured to correct for optical field distortions is configured to correct for at least one of field curvature, astigmatism, coma, or chromatic aberrations.
4. The optical assembly of claim 1 , wherein the optical assembly has an effective focal length of approximately 4 millimeters, and an f-number of greater than 5.
5. The optical assembly of claim 1 , wherein the first plastic aspheric lens of the first lens group has a first aspheric surface along the optical axis and a second aspheric surface opposite the first aspheric surface of the first plastic aspheric lens of the first lens group disposed along the optical axis, and wherein the first plastic aspheric lens of the first lens group is formed of a Crown type plastic having a positive optical power, and the second plastic aspheric lens of the first lens group has a first aspheric surface along the optical axis and a second aspheric surface along the optical axis, and wherein the second plastic aspheric lens of the first lens group is formed of a Flint type material having a negative optical power.
6. The optical assembly of claim 1 , wherein the first plastic aspheric lens of the second lens group has a first aspheric surface along the optical axis and a second aspheric surface opposite the first aspheric surface of the first plastic aspheric lens of the second lens group disposed along the optical axis, wherein the first plastic aspheric lens of the second lens group is formed of a Crown type plastic having a positive optical power, and wherein the second plastic aspheric lens of the second lens group is formed of a Flint type material having a negative optical power.
7. The optical assembly of claim 1 , wherein the second lens group comprises three aspheric plastic lenses.
8. The optical assembly of claim 1 , further comprising a lens holder with a front window, the lens holder configured to hold the aperture, the first lens group, glass lens, and the second lens group in position along the optical axis to provide the image to the imaging sensor.
9. The optical assembly of claim 1 , further comprising an illumination system configured to illuminate a target for imaging of the target.