Zoom lens and image pickup apparatus including same
A zoom lens includes a focus lens unit that moves in focus adjustment, a magnification lens unit including lens units that move in magnification, and a relay lens unit that does not move for magnification, in this order from the object side toward the image side, and a correction lens unit that is disposed in the focus lens unit or magnification lens unit and moves in the optical axis direction to correct displacement of the in-focus position. The amounts of change in in-focus position at the wide angle and telephoto ends with the correction lens unit moved by 1 mm in the optical axis direction, the maximum absolute value of the amount of movement of the correction lens unit for correcting displacement of the in-focus position, and the maximum absolute value of the amount of movement of the lens units in the magnification lens unit are set as appropriate.
1. A zoom lens comprising in order from an object side to an image side: a focus lens unit that moves for focus adjustment, a magnification lens group including two or more lens units that move for magnification, and a relay lens unit that does not move for magnification, wherein a correction lens unit is disposed in the focus lens unit or the magnification lens group and moves in an optical axis direction to correct displacement of an in-focus position of the zoom lens, and conditional expressions
0.001< Mb/Mm< 0.100,
0.005 <|ΔSkw|< 0.500, and
0.001<Δ Skw/ΔSkt|< 0.100
are satisfied, where ΔSkw is an amount (mm) of change in the in-focus position at a wide angle end with the correction lens unit moved by 1 mm in the optical axis direction, ΔSkt is an amount (mm) of change in the in-focus position at a telephoto end with the correction lens unit moved by 1 mm in the optical axis direction, Mb is a maximum absolute value of an amount of movement of the correction lens unit for correcting displacement of the in-focus position, and Mm is a maximum absolute value of amounts of movement of the lens units in the magnification lens group.
2. The zoom lens according to claim 1 , wherein the correction lens unit corrects one or more of displacement of the in-focus position due to a change in position of the lens units in the magnification lens group, displacement of the in-focus position due to a change in position of the focus lens unit, displacement of the in-focus position due to a change in temperature, displacement of the in-focus position due to a change in posture of the zoom lens, and displacement of the in-focus position due to a manufacturing error.
3. The zoom lens according to claim 1 , further comprising a stop between the magnification lens group and the relay lens unit,
wherein the correction lens unit corrects one or more of displacement of the in-focus position due to a change in position of the lens unit in the magnification lens group, displacement of the in-focus position due to a change in position of the focus lens unit, displacement of the in-focus position due to a change in temperature, displacement of the in-focus position due to a change in posture of the zoom lens, displacement of the in-focus position due to a manufacturing error, and displacement of the in-focus position due to a change in stop value of the stop.
4. The zoom lens according to claim 1 , wherein the correction lens unit is disposed in the focus lens unit.
5. The zoom lens according to claim 1 , wherein the correction lens unit is disposed in the magnification lens group.
6. The zoom lens according to claim 1 , wherein the correction lens unit consists of one lens, two lenses, or three lenses.
7. An image pickup apparatus comprising: a zoom lens comprising in order from an object side to an image side: a focus lens unit that moves for focus adjustment, a magnification lens group including two or more lens units that move for magnification, and a relay lens unit that does not move for magnification, wherein a correction lens unit is disposed in the focus lens unit or the magnification lens group and moves in an optical axis direction to correct displacement of an in-focus position of the zoom lens, and conditional expressions
0.001< Mb/Mm< 0.100,
0.005<|Δ Skw|< 0.500, and
0.001<Δ Skw/ΔSkt< 0.100
are satisfied, where ΔSkw is an amount (mm) of change in the in-focus position at a wide angle end with the correction lens unit moved by 1 mm in the optical axis direction, ΔSkt is an amount (mm) of change in the in-focus position at a telephoto end with the correction lens unit moved by 1 mm in the optical axis direction, Mb is a maximum absolute value of an amount of movement of the correction lens unit for correcting displacement of the in-focus position, and Mm is a maximum absolute value of amounts of movement of the lens units in the magnification lens group; and an image pickup element that receives an optical image formed by the zoom lens, wherein conditional expressions
D=Fno ×δ, and
1.0< Mb/D< 300.0
are satisfied, where Fno is a maximum aperture of the zoom lens, δ is a diameter (mm) of permissible circle of confusion of the image pickup apparatus, and D is a depth of focus.
8. The image pickup apparatus according to claim 7 , further comprising:
a zoom position detector that detects position of the lens units in the magnification lens group;
a focus position detector that detects position of the focus lens unit;
a stop value detector that detects stop value of a stop comprised in the zoom lens;
a temperature sensor that detects temperature;
a posture detector that detects posture of the zoom lens;
a correction position detector that detects position of the correction lens unit;
a driver that drives the correction lens unit; and
a controller that obtains an amount of one or more of displacement of the in-focus position by a change in position of the lens units in the magnification lens group, displacement of the in-focus position by a change in position of the focus lens unit, displacement of the in-focus position by a change in temperature, displacement of the in-focus position by a change in the stop value, and displacement of the in-focus position by a change in the posture, and controls moving of the correction lens unit based on the obtained amount.