Microscope objective lens, microscope optical system, and microscope device

A microscope objective lens consisting of a first lens group, a second lens group having positive refractive power, a third lens group having a concave surface facing an image side, and a fourth lens group having a concave surface facing an object side, the lens groups being arranged in order from the object side along an optical axis, wherein

• the first lens group consists of a plano-convex positive lens having a flat surface facing the object side and a negative lens, the lenses being arranged in order from the object side along the optical axis, and
• the third lens group consist of a positive lens and a negative lens having a concave surface facing an image side, the lenses being arranged in order from the object side along the optical axis,
• the following conditional expressions are satisfied,
• 20
• <
• ν
• ⁢
• dLe
• <
• 30
• 0
• <
• -
• 0.
• ⁢
• 035
• ×
• (
• ν
• ⁢
• dLe
• -
• 20
• )
• +
• 0
• .
• 6
• ⁢
• 3
• -
• θ
• ⁢
• gFLe
• where, vdLe:
• Abbe number of the final lens, and
• θgFLe:
• partial dispersion ratio of the final lens, which is defined by the following expression,
• θ
• ⁢
• gFLe
• =
• (
• ngLe
• -
• nFLe
• )
• /
• (
• nFLe
• -
• nCLe
• )
• where ngLe represents a refractive index of the final lens at a g-line, nFLe represents a refractive index of the final lens at an F-line, and nCLe represents a refractive index of the final lens at a C-line.