An optical probe and an optical system therefor are provided. The optical probe is includes a housing configured to house the optical system and the housing has a transparent window therein. the optical system includes a light emitting unit, a collimation lens, and a focusing lens. A numerical aperture of the optical system is adjustable by adjusting a pupil diameter of the collimation lens and a focal length of the focusing lens. The pupil diameter of the collimation lens is adjustable based on a variable focal lens or by adjusting a distance between the collimation lens and the light emitting unit.