Variable magnification optical system and imaging apparatus
A variable magnification optical system consists of, in order from an object side, a first optical system remaining stationary during changing magnification and a second optical system including a plurality of lens groups moving during changing magnification. The first optical system includes a first mirror and a second mirror having reflective surfaces arranged to face each other. The first mirror has a reflective surface concave toward the object side. The second mirror has a reflective surface convex toward the image side. An intermediate image is formed between the second mirror and the second optical system. Predetermined conditional expressions relating to the partial dispersion ratios of the lenses included in the second optical system are satisfied.
1. A variable magnification optical system consisting of, in order from an object side:
a first optical system that includes two reflecting mirrors having reflective surfaces arranged to face each other and remains stationary with respect to an image plane during changing magnification; and
a second optical system that includes at least two positive lenses and at least one negative lens,
wherein the two reflecting mirrors consist of
a first reflecting mirror that has a reflective surface concave toward the object side and reflects light, which is originated from an object, toward the object side, and
a second reflecting mirror that has a reflective surface convex toward an image side and reflects the reflected light, which is reflected from the first reflecting mirror, toward the image side,
wherein the second optical system includes, successively in order from a position closest to the object side,
a first lens group that consistently moves to the object side during changing magnification from a wide-angle end to a telephoto end and has a positive refractive power, and
a second lens group that moves in a direction of an optical axis with a locus different from a locus of the first lens group during changing magnification and has a positive refractive power,
wherein an intermediate image is formed between the second reflecting mirror and the first lens group, and the intermediate image is re-formed through the second optical system, and
wherein assuming that
an average value of partial dispersion ratios of all the positive lenses in the second optical system between a g line and an F line is θgFp, and
an average value of partial dispersion ratios of all the negative lenses in the second optical system between the g line and the F line is θgFn,
Conditional Expression (1) is satisfied,
−0.04<θ gFp−θgFn< 0.1 (1).
2. The variable magnification optical system according to claim 1 , wherein assuming that
an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp, and
an average value of Abbe numbers of all the negative lenses in the second optical system at the d line is νdn,
Conditional Expression (2) is satisfied,
10<ν dp−νdn< 40 (2).
3. The variable magnification optical system according to claim 1 , wherein assuming that
an average value of partial dispersion ratios of all the positive lenses in the second optical system between a C line and a t line is θCtp, and
an average value of the partial dispersion ratios of all the negative lenses in the second optical system between the C line and the t line is θCtn,
Conditional Expression (3) is satisfied,
−0.1<θ Ctp−θCtn< 0.1 (3).
4. The variable magnification optical system according to claim 1 , wherein the first optical system includes a field lens group that consists of two or less lenses and that has a positive refractive power and that is a lens component closest to the intermediate image.
5. The variable magnification optical system according to claim 1 , wherein the first reflecting mirror is an optical element having a power at a position closest to the object side on an optical path.
6. The variable magnification optical system according to claim 1 , wherein the first optical system includes a correction lens group consisting of two or less lenses which are disposed in an optical path from the first reflecting mirror to the second reflecting mirror and in an optical path from the second reflecting mirror to a position of the intermediate image and which have a common optical axis with respect to the first reflecting mirror and the second reflecting mirror.
7. The variable magnification optical system according to claim 1 , wherein assuming that an average value of the partial dispersion ratios of all the negative lenses in the second optical system between a C line and a t line is θCtn, Conditional Expression (4) is satisfied,
0.75<θ Ctn< 0.9 (4).
8. The variable magnification optical system according to claim 1 , wherein assuming that an average value of the partial dispersion ratios of all the positive lenses in the second optical system between the C line and the t line is θCtp, Conditional Expression (5) is satisfied,
0.75<θ Ctp< 0.9 (5).
9. The variable magnification optical system according to claim 1 , wherein assuming that an average value of Abbe numbers of all the negative lenses in the second optical system at a d line is νdn, Conditional Expression (6) is satisfied,
50<ν dn< 65 (6).
10. The variable magnification optical system according to claim 1 , wherein assuming that an average value of refractive indices of all the negative lenses in the second optical system at a d line is Ndn, Conditional Expression (7) is satisfied,
1.5< Ndn< 1.75 (7).
11. The variable magnification optical system according to claim 1 , wherein Conditional Expression (8) is satisfied,
0.53<θ gFn< 0.58 (8).
12. The variable magnification optical system according to claim 1 , wherein Conditional Expression (9) is satisfied,
0.5<θ gFp< 0.65 (9).
13. The variable magnification optical system according to claim 1 , wherein assuming that an average value of Abbe numbers of all the positive lenses in the second optical system at a d line is νdp, Conditional Expression (10) is satisfied,
70<ν dp< 100 (10).
14. The variable magnification optical system according to claim 1 , wherein assuming that an average value of refractive indices of all the positive lenses in the second optical system at a d line is Ndp, Conditional Expression (11) is satisfied,
1.43< Ndp< 1.75 (11).
15. The variable magnification optical system according to claim 1 , wherein Conditional Expression (1-1) is satisfied,
−0.02<θ gFp−θgFn< 0.06 (1-1).
16. The variable magnification optical system according to claim 2 , wherein Conditional Expression (2-1) is satisfied,
14<ν dp−νdn< 35 (2-1).
17. The variable magnification optical system according to claim 3 , wherein Conditional Expression (3-1) is satisfied,
−0.07<θ Ctp−θCtn< 0.05 (3-1).
18. The variable magnification optical system according to claim 7 , wherein Conditional Expression (4-1) is satisfied,
0.77<θ Ctn< 0.85 (4-1).
19. The variable magnification optical system according to claim 8 , wherein Conditional Expression (5-1) is satisfied,
0.78<θ Ctp< 0.85 (5-1).
20. An imaging apparatus comprising the variable magnification optical system according to claim 1 .