Fixed focal length lens and image pickup apparatus
A fixed focal length lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit and a third lens unit, wherein the first lens unit does not move for focusing, at least the second lens unit moves for focusing, a distance between each pair of adjacent lens units changes for focusing, and the first lens unit includes two negative lenses disposed in succession from the object side, and wherein a focal length of the fixed focal length lens, a focal length of the first lens unit, and a combined focal length of the two negative lenses of the first lens unit are appropriately set.
1. A fixed focal length lens comprising, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit, wherein the first lens unit does not move for focusing, at least the second lens unit moves for focusing, a distance between each pair of adjacent lens units changes for focusing, and the first lens unit includes two negative lenses disposed in succession from the object side, and wherein
conditional expressions
1.0< f 1/ f< 6.5, and
0.05<| f 1 n|/f 1<0.22
are satisfied where f represents a focal length of the fixed focal length lens, f1 represents a focal length of the first lens unit, and f1n represents a combined focal length of the two negative lenses of the first lens unit.
2. The fixed focal length lens according to claim 1 , wherein
a conditional expression
0.3<| f 11|/ f 1<1.0
is satisfied where f11 represents a focal length of a first lens, disposed on the object side, of the two negative lenses.
3. The fixed focal length lens according to claim 1 , wherein
a conditional expression
0.1<| f 12|/ f 1<0.7
is satisfied where f12 represents a focal length of a second lens, disposed on the image side, of the two negative lenses.
4. The fixed focal length lens according to claim 1 , wherein
a conditional expression
−1.5<( R 11 i+R 12 o )/( R 11 i−R 12 o )<0
is satisfied where R11i represents a radius of curvature of a surface on the image side of a first lens, disposed on the object side, of the two negative lenses, and R12o represents a radius of curvature of a surface on the object side of a second lens, disposed on the image side, of the two negative lenses.
5. The fixed focal length lens according to claim 1 , wherein
a conditional expression
50< v 11<80
is satisfied where v11 represents an Abbe number of a first lens, disposed on the object side, of the two negative lenses.
6. The fixed focal length lens according to claim 1 , wherein
a conditional expression
1.70< N 12<2.10
is satisfied where N12 represents a refractive index of a second lens, disposed on the image side, of the two negative lenses.
7. The fixed focal length lens according to claim 1 , wherein
the first lens unit includes a sub lens unit disposed on the image side of the two negative lenses, and
a conditional expression
1.0< f 1 p/|f 1 n|< 3.0
is satisfied where f1p represents a focal length of the sub lens unit.
8. The fixed focal length lens according to claim 1 , wherein
the first lens unit includes a sub lens unit disposed on the image side of the two negative lenses,
the sub lens unit includes at least one positive lens, and
a conditional expression
1.6< N 1pave<2.0
is satisfied where N1pave represents an average refractive index of positive lenses included in the sub lens unit.
9. The fixed focal length lens according to claim 1 , wherein
the third lens unit is configured to move differently from the second lens unit for focusing, and
a conditional expression
0.4<| m 2|/| m 3|<2.0
is satisfied where m2 and m3 respectively represent a movement amount of the second lens unit and a movement amount of the third lens unit required for shift from a case of focusing on an object at infinity to a case of focusing on a closest object.
10. An image pickup apparatus comprising:
a fixed focal length lens comprising, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit, wherein the first lens unit does not move for focusing, at least the second lens unit moves for focusing, a distance between each pair of adjacent lens units changes for focusing, and the first lens unit includes two negative lenses disposed in succession from the object side, and wherein
conditional expressions
1.0< f 1/ f< 6.5, and
0.05<| f 1 n|/f 1<0.22
are satisfied where f represents a focal length of the fixed focal length lens, f1 represents a focal length of the first lens unit, and f1n represents a combined focal length of the two negative lenses of the first lens unit, and
an image pickup element arranged on an image plane of the fixed focal length lens.