Sample observation device and sample observation method

An observation device for observing a sample, the observation device comprising:

• an illumination optical system;
• and
• an observation optical system,
• wherein:
• the illumination optical system includes a light source, a condenser lens, and an aperture member,
• the observation optical system includes an objective lens and an imaging lens,
• the aperture member has a light-shielding part or a darkening part, and a transmission part,
• the aperture member is disposed so that the light-shielding part or the darkening part includes an optical axis of the illumination optical system,
• the transmission part is located outside of an outer edge of the light-shielding part or the darkening part,
• an image of the transmission part of the aperture member is formed approximately at a pupil position of the objective lens,
• an image of an inner edge of the transmission part is formed inside of an outer edge of a pupil of the objective lens,
• an image of an outer edge of the transmission part is formed outside of the outer edge of the pupil of the objective lens,
• when the sample is present, the image of the transmission part is decentered relative to the pupil of the objective lens due to refraction caused by the sample, and
• the following conditional expressions are satisfied:
• 0.005≤Ratio≤0.9, and
• 1.1≤I0.1/I0
• where:
• Ratio=(Rob−R0×β)/(R1×β−Rob);
• R0 denotes a length from the optical axis of the illumination optical system to the inner edge of the transmission part;
• R1 denotes a length from the optical axis of the illumination optical system to the outer edge of the transmission part;
• Rob denotes a radius of the pupil of the objective lens;
• β denotes a value obtained by dividing a focal length of the objective lens by a focal length of the condenser lens;
• I0.1 denotes a quantity of light passing through the pupil of the objective lens when Δd=0.1×Rob;
• I0 denotes a quantity of light passing through the pupil of the objective lens when Δd=0;
• and
• Δd denotes an amount of displacement of the image of the transmission part of the aperture member relative to the pupil of the objective lens.