Observation or measurement means and observation or measurement system provided with the same, feeble light image pickup optical system and microscope apparatus provided with the same, microscope system provided with the microscope apparatus, and observation apparatus and observation system provided with the same

Abstract

An observation or measurement device has, at least, an infinity-corrected objective lens and an imaging lens, and satisfies a condition, 4.56≦D·NA'≦30 (mm), where D is the parfocal distance of the objective lens and NA′ is the numerical aperture of the imaging lens. It is desirable to make a distance from the mount position of the objective lens to the most object-side surface of the imaging lens variable and to satisfy a condition, 0.5 FL<W<1.2 FL (mm), where W is the variable amount of the distance from the mount position of the objective lens to the most object-side surface of the imaging lens, and FL is the focal length of the imaging lens. It is more desirable to satisfy conditions, 0.4<D/FL<5 and 1≦D/φd<3, where φd is the outside diameter of a connection at the mount of the objective lens.