Patent ID: 11899280
Assignee: TAMRON CO., LTD.
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. An optical system comprising:
a focus lens group having positive refractive power and configured to move along an optical axis when focusing from an infinite-distance object to a short-distance object, wherein
the focus lens group integrally moves when focusing, and includes a lens subgroup A, an aperture stop, and a lens subgroup B in order from an object side,
the lens subgroup A includes a negative lens, a positive lens, and a positive lens in order from an image side,
the lens subgroup B includes a negative lens and a positive lens in order from the object side, and
the optical system satisfies following conditional expressions:

−0.045<θIRp−θIRn<0.045  (1)

0.50<Fb/F<2.50  (2)

where
θIRp is an average value of (nF−nd)/(n1700 nm−nd) of all positive lenses disposed in the lens subgroup B,
θIRn is an average value of (nF−nd)/(n1700 nm−nd) of all negative lenses disposed in the lens subgroup B,
nF is a refractive index on an F line,
nd is a refractive index on a d line,
n1700 nm is a refractive index at a wavelength of 1700 nm,
Fb is a focal length on the d line of the lens subgroup B, and
F is a focal length on the d line of the optical system.