A zoom lens includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in order from an object side. In a case of magnification, the first lens group, the second lens group, and the third lens group move. The third lens group consists of a third a lens group that does not move in a case of image shake correction, a third b lens group that moves in the case of the image shake correction, and a third c lens group that does not move in the case of the image shake correction in order from the object side. The third b lens group consists of a positive lens and a negative lens. A predetermined conditional expression related to the third b lens group is satisfied.

A zoom lens includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in order from an object side. In a case of magnification, the first lens group, the second lens group, and the third lens group move. The third lens group consists of a third a lens group that does not move in a case of image shake correction, a third b lens group that moves in the case of the image shake correction, and a third c lens group that does not move in the case of the image shake correction in order from the object side. The third b lens group consists of a positive lens and a negative lens. A predetermined conditional expression related to the third b lens group is satisfied.

The zoom lens includes a positive first lens group, a negative second lens group, a positive third lens group, a negative fourth lens group, a negative fifth lens group, and a positive sixth lens group in order from an object side. All distances between adjacent lens groups change during zooming. The first lens group consists of a negative lens, a positive lens, and a positive lens in order from the object side. Only the fourth lens group moves to an image side during focusing from a long range to a short range. Conditional Expression related to a distance from a lens surface of the first lens group closest to the object side to an image plane and a distance from a lens surface of the second lens group closest to the object side to the image plane is satisfied.

A method for ascertaining an alignment of a lens system. The method include: aligning the lens system according to a provided first alignment; ascertaining a first refracted optical signal, the first refracted optical signal being ascertained by a refraction of a first emitted optical signal at the lens system (aligned according to the first alignment; ascertaining a first attribute value, the first attribute value characterizing an attribute of the first refracted optical signal; training a first machine learning system as a function of the first alignment and the ascertained first attribute value, the machine learning system being designed to ascertain an output for an alignment that characterizes the attribute of the alignment; ascertaining the alignment of the lens system based on an output of the first machine learning system.

A method for ascertaining an alignment of a lens system. The method include: aligning the lens system according to a provided first alignment; ascertaining a first refracted optical signal, the first refracted optical signal being ascertained by a refraction of a first emitted optical signal at the lens system (aligned according to the first alignment; ascertaining a first attribute value, the first attribute value characterizing an attribute of the first refracted optical signal; training a first machine learning system as a function of the first alignment and the ascertained first attribute value, the machine learning system being designed to ascertain an output for an alignment that characterizes the attribute of the alignment; ascertaining the alignment of the lens system based on an output of the first machine learning system.

A lens apparatus includes two optical systems. Each of the two optical systems includes, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a first reflective surface, a second reflective surface, and a rear lens unit having positive refractive power. At least a distance between the first lens unit and the second lens unit and a distance between the second lens unit and the first reflective surface are changed during magnification variation. A predetermined condition is satisfied.

A lens apparatus includes two optical systems. Each of the two optical systems includes, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a first reflective surface, a second reflective surface, and a rear lens unit having positive refractive power. At least a distance between the first lens unit and the second lens unit and a distance between the second lens unit and the first reflective surface are changed during magnification variation. A predetermined condition is satisfied.

An image capturing lens system includes four lens groups which include eight lens elements. The four lens groups are, in order from an object side to an image side: first, second, third and fourth lens groups. The eight lens elements are, in order from the object side to the image side: first, second, third, fourth, fifth, sixth, seventh and eighth lens elements. The first and second lens elements respectively have positive and negative refractive power. At least one lens element in the second through fourth lens groups has an inflection point. A focal length of the image capturing lens system is varied by changing axial distances between the four lens groups in a zooming process. The second lens group is moved relative to the first lens group along an optical axis in the zooming process. The image capturing lens system has a long-focal-length end and a short-focal-length end.

An image capturing lens system includes four lens groups which include eight lens elements. The four lens groups are, in order from an object side to an image side: first, second, third and fourth lens groups. The eight lens elements are, in order from the object side to the image side: first, second, third, fourth, fifth, sixth, seventh and eighth lens elements. The first and second lens elements respectively have positive and negative refractive power. At least one lens element in the second through fourth lens groups has an inflection point. A focal length of the image capturing lens system is varied by changing axial distances between the four lens groups in a zooming process. The second lens group is moved relative to the first lens group along an optical axis in the zooming process. The image capturing lens system has a long-focal-length end and a short-focal-length end.

Provided is a zoom lens, including, in order from an object side, a positive first lens unit, a negative second lens unit, a positive third lens unit, a negative fourth lens unit, and a positive fifth lens unit, in which an interval between each pair of adjacent lens units is changed during zooming, in which the second lens unit moves during focusing, and includes, in order from the object side to the image side, a negative lens, a negative lens, a positive lens, and a negative lens, and in which a focal length of the second lens unit, a thickness of the second lens unit on an optical axis, a refractive index of a material of the positive lens included in the second lens unit, and an average value of refractive indices of materials of the negative lenses included in the second lens unit are each appropriately set.