Imaging optical system and optical apparatus including the same
An imaging optical system includes an aperture stop, a first cemented lens, a second cemented lens, and a third cemented lens, and the first cemented lens is positioned closer to the enlargement side than the aperture stop is, the second cemented lens is positioned on the reduction side and adjacent to a predetermined lens unit is, and the third cemented lens is positioned closer to the reduction side than the aperture stop is, the predetermined lens unit has a negative refractive power and includes all of lenses located from a lens positioned closest to the enlargement side to the first cemented lens, the first cemented lens includes a positive lens and a negative lens, the second cemented lens includes a negative lens and a positive lens, and the third cemented lens includes a positive lens and a negative lens.
1. An imaging optical system configured to form a conjugate relation between a conjugate point on an enlargement side having a long distance and a conjugate point on a reduction side having a short distance,
the imaging optical system comprising:
an aperture stop;
a first cemented lens;
a second cemented lens; and
a third cemented lens,
wherein
the first cemented lens is positioned closer to the enlargement side than the aperture stop is,
the second cemented lens is positioned closer to the reduction side than a predetermined lens unit is, and adjacent to the predetermined lens unit,
the third cemented lens is positioned closer to the reduction side than the aperture stop is,
the predetermined lens unit has a negative refractive power and includes all of lenses located from a lens positioned closest to the enlargement side to the first cemented lens,
the first cemented lens includes, in order from the enlargement side, a positive lens and a negative lens and has a surface closest to the reduction side having a concave surface facing toward the reduction side,
the second cemented lens includes, in order from the enlargement side, a negative lens and a positive lens and has a surface closest to the enlargement side having a concave surface facing toward the enlargement side,
the third cemented lens includes, in order from the enlargement side, a positive lens and a negative lens,
one or two moving lens units only moving at a time of focusing are included, and
the lenses other than the moving lens units are fixed.
2. The imaging optical system according to claim 1 , wherein
the lens positioned closest to the enlargement side is a first negative lens, and
the first negative lens is a meniscus lens.
3. The imaging optical system according to claim 2 , wherein
following Conditional Expression (1) is satisfied:
1<( R N1F +R N1R )/( R N1F −R N1R )<10 (1),
where
R N1F is a paraxial radius of curvature of an enlargement-side surface of the first negative lens; and
R N1R is a paraxial radius of curvature of a reduction-side surface of the first negative lens.
4. The imaging optical system according to claim 1 , wherein
a lens component is a lens block in which only an enlargement-side surface and a reduction-side surface are in contact with air in an optical path, and
one or more positive lens components is provided between the second cemented lens and the third cemented lens.
5. The imaging optical system according to claim 1 , wherein
first positive lens positioned closest to the second cemented lens is further included, and
following Conditional Expression (2) is satisfied:
0<( R P1F +R P1R )/( R P1F −R P1R )<3 (2),
where
R P1F is a paraxial radius of curvature of an enlargement-side surface of the first positive lens; and
R P1R is a paraxial radius of curvature of a reduction-side surface of the first positive lens.
6. The imaging optical system according to claim 1 , wherein
a second negative lens and a second positive lens are further included in order from the reduction side,
the second negative lens is a meniscus lens, and
following Conditional Expression (3) is satisfied:
0.01<( R P2F +R P2R )/( R P2F −R P2R )<3 (3),
where
R P2F is a paraxial radius of curvature of an enlargement-side surface of the second positive lens; and
R P2R is a paraxial radius of curvature of a reduction-side surface of the second positive lens.
7. The imaging optical system according to claim 1 , wherein Conditional Expression (4) below is satisfied:
−10<( R NGF +R NGR )/( R NGF −R NGR )<20 (4),
where
R NGF is a paraxial radius of curvature of a surface positioned closest to the enlargement side in the predetermined lens unit; and
R NGR is a paraxial radius of curvature of a surface positioned closest to the reduction side in the predetermined lens unit.
8. The imaging optical system according to claim 1 , wherein Conditional Expression (5) below is satisfied:
−1.5<( R NGR +R C2F )/( R NGR −R C2F )<5 (5),
where
R NGR is a paraxial radius of curvature of a surface positioned closest to the reduction side in the predetermined lens unit; and
R C2F is a paraxial radius of curvature of a surface positioned closest to the enlargement side in the second cemented lens.
9. The imaging optical system according to claim 2 , wherein
following Conditional Expression (A) is satisfied:
0< f/e N1F <2 (A),
where
f is a focal length of the imaging optical system as a whole at a time of focusing to an object at infinity; and
e N1F is a maximum effective aperture of an enlargement-side surface of the first negative lens.
10. The imaging optical system according to claim 1 , wherein
following Conditional Expression (B) is satisfied:
0<( f/e AS )/ Fno< 2 (B),
where
f is a focal length of the imaging optical system as a whole at a time of focusing to an object focusing at infinity;
e AS is a maximum diameter of the aperture stop; and
Fno is an F-number of the imaging optical system as a whole at the time of focusing to the object focusing at infinity.
11. The imaging optical system according to claim 1 , wherein
following Conditional Expression (C) is satisfied:
0< T air _ max /Σd≤ 0.27 (C),
where
T air _ max is a largest axial air space in a range from a surface positioned closest to the enlargement side to a surface positioned closest to the reduction side in the imaging optical system; and
Σd is an axial distance from the surface positioned closest to the enlargement side to the surface positioned closest to the reduction side in the imaging optical system.
12. The imaging optical system according to claim 1 , wherein
the imaging optical system further comprises a first focusing lens unit, and
the first focusing lens unit is disposed closer to the reduction side than the third cemented lens is, moves along an optical axis of the imaging optical system at a time of the focusing, and has a negative refractive power.
13. The imaging optical system according to claim 12 , wherein the first focusing lens unit satisfies following Conditional Expression (D):
0<( R F1F +R F1R )/( R F1F −R F1R )<5 (D),
where
R F1F is a paraxial radius of curvature of a surface positioned closest to the enlargement side in the first focusing lens unit; and
R F1R is a paraxial radius of curvature of a surface positioned closest to the reduction side in the first focusing lens unit.
14. The imaging optical system according to claim 12 , wherein
the first focusing lens unit moves toward the reduction side at a time of focusing to an object at a close distance from a state of focusing on an object at infinity which positions on the enlargement side, and
Conditional Expression (E) below is satisfied:
−1< M F1 /f< 0 (E),
where
M F1 is a maximum amount of movement along the optical axis direction at the time of focusing in the first focusing lens unit; and
f is a focal length of the imaging optical system as a whole at the time of focusing to the object at infinity.
15. The imaging optical system according to claim 12 , wherein
the imaging optical system further comprises a second focusing lens unit, and
the second focusing lens unit is disposed closer to the reduction side than the first focusing lens unit is, moves along the optical axis of the imaging optical system while changing a distance to the first focusing lens unit at the time of focusing, and has a positive refractive power.
16. The imaging optical system according to claim 15 , wherein the first focusing lens unit and the second focusing lens unit each include at most two lenses.
17. The imaging optical system according to claim 15 , wherein
the first focusing lens unit moves toward the reduction side at the time of focusing to an object at a close distance from a state of focusing on an object at infinity which positions on the enlargement side,
the second focusing lens unit moves toward the enlargement side at the time of focusing to the object at a close distance from the state of focusing on the object at infinity which positions on the enlargement side, and
the first focusing lens unit and the second focusing lens unit satisfy following Conditional Expression (F) at the time of focusing:
0< M F2 /M F1 <1.5 (F),
where
M F1 is a maximum amount of movement along the optical axis direction at the time of the focusing in the first focusing lens unit; and
M F2 is a maximum amount of movement along the optical axis direction at the time of the focusing in the second focusing lens unit.
18. The imaging optical system according to claim 15 , wherein the first focusing lens unit and the second focusing lens unit satisfy following Conditional Expression (G):
−3< f F1 /f F2 <−0.5 (G),
where
f F1 is a focal length of the first focusing lens unit; and
f F2 is a focal length of the second focusing lens unit.
19. The imaging optical system according to claim 15 , wherein the first focusing lens unit and the second focusing lens unit satisfy following Conditional Expression (H):
5<β F1 /β F2 <50 (H),
where
β F1 is a lateral magnification of the first focusing lens unit at the time of focusing to an object at infinity; and
β F2 is a lateral magnification of the second focusing lens unit at the time of focusing to the object at infinity.
20. An optical apparatus comprising:
an optical system; and
an image pickup element arranged on a reduction side,
wherein
the image pickup element has an image pickup surface and converts an image formed on the image pickup surface by the optical system into an electrical signal, and
the optical system is the imaging optical system of claim 1 .
21. An optical apparatus comprising:
an optical system; and
a display element arranged on a reduction side,
wherein
the display element has a display surface,
an image displayed on the display surface is projected toward an enlargement side by the optical system, and
the optical system is the imaging optical system of claim 1 .