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

Claim 2:
3. The optical system according to claim 1, wherein the lens subgroup B includes at least one negative lens that satisfies following conditional expressions:

θct≥0.800  (7)

vd≤55  (8)

wherein
θct is a partial dispersion ratio from a C line to a t line of the negative lens, and
the 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,
nt is a refractive index on the t line, and
vd is an Abbe number on the d line.