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

Claim 1:
2. The optical system according to claim 1 that satisfies a following conditional expression:

−0.007<0.00558×vd_n+0.531−θct_n<0.000  (3)

where
vd_n is an Abbe number on the d line of the negative lens disposed on the most object side in the lens subgroup B,
θct_n is a partial dispersion ratio regarding a C line and a t line of the negative lens disposed on the most object side in the lens subgroup B, and
a partial dispersion ratio θct from the C line to the t line is defined by a following expression:

θct=(nC−nt)/(nF−nC)

nC is a refractive index on the C line, and
nt is a refractive index on the t line.