Image forming lens system and image pickup apparatus including the same

An image forming lens system comprising, in order from an object side to an image side:

• a first lens unit having a positive refractive power;
• a second lens unit having a negative refractive power;
• and
• a third lens unit,
• wherein:
• the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
• the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
• the third lens unit includes a positive lens element,
• the rear-side lens unit includes a negative lens element and a positive lens element,
• the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
• the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis,
• a lens element closest to the object side in the first lens unit is fixed in position,
• an aperture stop that restricts on-axis luminous flux is disposed between the first lens unit and the second lens unit, and
• the following Conditional Expression (9-1) is satisfied:
• 0.04≤|fG2/f|≤0.41 (9-1)
• where
• fG2 is a focal length of the second lens unit,
• f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance, and
• a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.

An image forming lens system comprising, in order from an object side to an image side:

• a first lens unit having a positive refractive power;
• a second lens unit having a negative refractive power;
• and
• a third lens unit,
• wherein:
• the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
• the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
• the third lens unit has a positive lens element,
• each lens element in the front-side lens unit is a lens element that satisfies the following Conditional Expression (a),
• the rear-side lens unit includes a negative lens element and a positive lens element,
• the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
• the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, and
• the following Conditional Expression (1) is satisfied:
• −0.7≤f/fLens (a)
• 0.015≤ΔGFGR/f≤0.25 (1)
• where
• f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
• fLens is a focal length of each lens element in the front-side lens unit,
• ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit, and
• a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.

An image forming lens system comprising, in order from an object side to an image side:

• a first lens unit having a positive refractive power;
• a second lens unit having a negative refractive power;
• and
• a third lens unit,
• wherein:
• the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
• the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
• the third lens unit includes a positive lens element,
• each lens element in the front-side lens unit does not include a predetermined negative lens element that satisfies the following Conditional Expression (b),
• the rear-side lens unit includes a negative lens element and a positive lens element,
• the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
• the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, and
• the following Conditional Expression (1) is satisfied:
• 0.02≤DNx/φenp (b)
• 0.015≤ΔGFGR/f≤0.25 (1)
• where
• DNx is a thickness on an optical axis of the predetermined negative lens element,
• φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance,
• f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
• ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit, and
• a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.

An image forming lens system comprising, in order from an object side to an image side:

• a first lens unit having a positive refractive power;
• a second lens unit having a negative refractive power;
• and
• a third lens unit,
• wherein:
• the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
• the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
• the third lens unit includes a positive lens element,
• the rear-side lens unit includes a negative lens element and a positive lens element,
• each lens element in the front-side lens unit is a lens element that satisfies the following Conditional Expression (a), or
• each lens element in the front-side lens unit does not include a predetermined negative lens element that satisfies following the Conditional Expression (b), and
• the following Conditional Expressions (1), (9-2), and (3″) are satisfied:
• −0.7≤f/fLens (a)
• 0.02≤DNx/φenp (b)
• 0.015≤ΔGFGR/f≤0.25 (1)
• 0.06≤|fG2/f|≤0.22 (9-2)
• 77≤νdGFave (3″)
• where
• f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
• fLens is a focal length of each lens element in the front-side lens unit,
• DNx is a thickness on an optical axis of the predetermined negative lens element,
• φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance,
• ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit,
• fG2 is a focal length of the second lens unit,
• νdGFave is an average Abbe number of positive lens elements in the front-side lens unit, and
• a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.