An imaging lens system includes a first group having positive power and a second group having positive power disposed in that order from an object side to an image. The first group includes a first sub-group and a second sub-group. The second group includes a third sub-group, a stop, and a fourth sub-group. Conditional expressions (1), (2), and (3) below are satisfied:
0.07<f2/f1<0.4  (1);
0.45<f2/f2a<0.7  (2); and
1.05<f/R1aN<1.55  (3) where f denotes a focal length of an entirety of the imaging lens system focused at infinity, f1 denotes a focal length of the first group, f2 denotes a focal length of the second group focused at infinity, f2a denotes a focal length of the third sub-group focused at infinity, and R1aN denotes a radius of curvature of a surface closest to the image side within the first sub-group.

An optical system images an object with light with a wavelength of 8 μm or higher, and includes a diaphragm and an optical element having an aspherical surface and disposed at a position different from that of the diaphragm. In a section including an optical axis, a thickness of an optical element monotonously increases from an on-axis to an outermost off-axis or the optical element is the thinnest at a position other than an on-axis and an outermost off-axis. A predetermined condition is satisfied.

An optical system images an object with light with a wavelength of 8 μm or higher, and includes a diaphragm and an optical element having an aspherical surface and disposed at a position different from that of the diaphragm. In a section including an optical axis, a thickness of an optical element monotonously increases from an on-axis to an outermost off-axis or the optical element is the thinnest at a position other than an on-axis and an outermost off-axis. A predetermined condition is satisfied.

A light source optical system used with an excitation light source configured to emit first color light includes a wavelength conversion unit configured to receive the first color light emitted by the excitation light source and emit second color light with a wavelength different from a wavelength of the first color light, There is a first optical system having a positive power and a second optical system having a positive power provided in this order in an optical path between the excitation light source and the wavelength conversion unit. When a ray parallel to an optical axis of the first optical system is incident on the first optical system, a ray emitted from the first optical system is incident on the second optical system while approaching the optical axis. The second optical system has under-corrected spherical aberration at a paraxial focal position of the second optical system.

A light source optical system used with an excitation light source configured to emit first color light includes a wavelength conversion unit configured to receive the first color light emitted by the excitation light source and emit second color light with a wavelength different from a wavelength of the first color light, There is a first optical system having a positive power and a second optical system having a positive power provided in this order in an optical path between the excitation light source and the wavelength conversion unit. When a ray parallel to an optical axis of the first optical system is incident on the first optical system, a ray emitted from the first optical system is incident on the second optical system while approaching the optical axis. The second optical system has under-corrected spherical aberration at a paraxial focal position of the second optical system.

An optical system includes in order from an object side to an image side: a front lens unit having a positive refractive power; and a rear lens unit including a lens having a positive refractive power, in which the front lens unit includes a lens arranged closest to the object side has a negative refractive power, an interval between the front lens unit and the rear lens unit changes for focusing, a radius of curvature of an object-side surface of the lens having the positive refractive power arranged closest to the image side a radius of curvature on an object-side surface of the lens having the positive refractive power arranged closest to the image side are appropriately set.

An optical system includes in order from an object side to an image side: a front lens unit having a positive refractive power; and a rear lens unit including a lens having a positive refractive power, in which the front lens unit includes a lens arranged closest to the object side has a negative refractive power, an interval between the front lens unit and the rear lens unit changes for focusing, a radius of curvature of an object-side surface of the lens having the positive refractive power arranged closest to the image side a radius of curvature on an object-side surface of the lens having the positive refractive power arranged closest to the image side are appropriately set.

An image sensor and well structure associated with and extending away from the surface of the image sensor are provided in various apparatuses, methods, and systems for determining the position of a light emitter located in object space. An exemplary method includes (i) providing the image sensor and structure associated therewith, the structure defining a field of view for each pixel within the array of pixels; (ii) determining a light intensity value for photoactivated pixels receiving light from the light emitter; (iii) identifying a first photoactivated pixel having a local maximum of light intensity; (iv) calculating a perpendicular distance between the first photoactivated pixel and the light emitter; and (v) constructing the position of the light emitter based on a position of the first photoactivated pixel in the array of pixels and the perpendicular distance between the first photoactivated pixel and the light emitter.

An image sensor and well structure associated with and extending away from the surface of the image sensor are provided in various apparatuses, methods, and systems for determining the position of a light emitter located in object space. An exemplary method includes (i) providing the image sensor and structure associated therewith, the structure defining a field of view for each pixel within the array of pixels; (ii) determining a light intensity value for photoactivated pixels receiving light from the light emitter; (iii) identifying a first photoactivated pixel having a local maximum of light intensity; (iv) calculating a perpendicular distance between the first photoactivated pixel and the light emitter; and (v) constructing the position of the light emitter based on a position of the first photoactivated pixel in the array of pixels and the perpendicular distance between the first photoactivated pixel and the light emitter.

The imaging lens comprises, successively in order from the object side, a positive first lens group that does not move during focusing, a second lens group that moves during focusing, a stop, and a positive third lens group that consists of all lenses moving integrally with the second lens group during focusing. The composite focal length of the second lens group and the third lens group is positive. The first lens group includes four or more positive lenses and three or more negative lenses. The imaging lens satisfies predetermined conditional expressions.