Patent ID: 8174686

Claim:
A focal position determining method for determining a focal position of an objective lens focused on an observed target region in a specimen, the method comprising: irradiating a living specimen with a visible light, the living specimen being imaged while moving the objective lens; measuring a focal position of the objective lens; calculating an irradiance contrast from a difference between a maximum value and a minimum value of pixel values of each pixel composing an irradiance image based on the imaged irradiated living specimen; determining a second focal position of the objective lens focused on an observed target region based on the calculated irradiance contrast and the measured focal position of the objective lens; stopping the light irradiance of the living specimen after determining the second focal position of the objective lens; imaging the living specimen with the objective lens at the determined second focal position, the living specimen being imaged using luminescence from the living specimen while not irradiating the living specimen; moving the objective lens and measuring a luminescence focal position of the objective lens; calculating a luminescence contrast based on the luminescent image; and re-determining the second focal position of the objective lens based on the calculated luminescence contrast and the measured luminescence focal position.