Objective

An objective comprising:

• a first lens group having positive refractive power;
• a second lens group having negative refractive power;
• and
• a third lens group having the positive refractive power and including two or more lens components,
• the first lens group, the second lens group, and the third lens group being sequentially disposed from an object side, wherein
• the first lens group includes:
• a meniscus-shaped first lens having the positive refractive power, the first lens having a concave surface facing an image side;
• and
• a meniscus-shaped second lens having the positive refractive power, the second lens having a concave surface facing the image side,
• the second lens group includes two or more positive lenses and one or more negative lenses,
• a total number of lenses included in the second lens group is seven or more,
• the objective satisfies following conditional expressions:
• 1.6
• ≤
• fL
• /
• TTL
• ≤
• 5
• (
• 1
• )
• 2
• ≤
• ER
• ⁢
• 1
• ⁢
• F
• /
• ER
• ⁢
• 2
• ⁢
• F
• (
• 2
• )
• 1.29
• ≤
• ER
• ⁢
• 3
• ⁢
• F
• /
• ER
• ⁢
• 2
• ⁢
• R
• ,
• (
• 3
• )
• a surface of the second lens group, the surface being situated closest to the object side, is, among surfaces having an effective radius of ER1F/2 or less of the objective, a surface situated closest to the object side,
• a surface of the third lens group, the surface being situated closest to the object side, is, among the surfaces having an effective radius of 1.29×ER2R or more of the objective, a surface situated closest to the object side, and
• wherein fL is a focal length of the objective, TTL is a distance on an optical axis of the objective from a surface of the objective, the surface being situated closest to the object side, to a surface of the objective, the surface being situated closest to the image side, ER1F is an effective radius of the surface of the objective, the surface being situated closest to the object side, ER2F is an effective radius of the surface of the second lens group, the surface being situated closest to the object side, ER2R is an effective radius of a surface of the second lens group, the surface being situated closest to the image side, and ER3F is an effective radius of the surface of the third lens group, the surface being situated closest to the object side.