Method and imaging apparatus

An imaging apparatus for tomographically imaging an imaging object in a medium carried in a container having an optically transparent wall part, the imaging apparatus comprising:

• an imaging unit which causes one branch light branched from low coherence light emitted from a light source to be incident on the imaging object, detects interference light generated by interference of signal light obtained by condensing reflected light from the imaging object via the wall part by an objective optical system and reference light obtained by reflecting another branch light by a reference mirror and outputs an interference signal corresponding to the detected interference light;
• a signal processor which obtains a reflected light intensity distribution of the imaging object based on the interference signal and generates a tomographic image from the reflected light intensity distribution;
• a focus position adjuster which changes a focus position of the objective optical system in an optical axis direction of the objective optical system;
• a mirror position adjuster which changes a position of the reference mirror in a direction along an optical path of the reference light;
• and a focus position calculator which calculates a focus position of the objective optical system in the tomographic image, wherein when:
• an object optical path length is defined as an optical path length of the signal light;
• a reference optical path length is defined as an optical path length of the reference light;
• a first adjustment amount is defined as a focus position adjustment amount of the objective optical system by the focus position adjuster when the objective optical system is focused on a first principal surface on a side of the objective optical system out of principal surfaces of the wall part;
• a second adjustment amount is defined as a focus position adjustment amount of the objective optical system by the focus position adjuster at which an intensity of reflected light from a second principal surface on a side of the imaging object out of the principal surfaces of the wall part is maximized when the reference mirror is positioned by the mirror position adjuster at a position where the reference optical path length is equal to the object optical path length to the first principal surface with the focus position adjustment amount of the objective optical system set at the first adjustment amount;
• and
• a first distance is defined as a distance between the first principal surface and the second principal surface in an optical axis direction of the objective optical system in the reflected light intensity distribution obtained from the interference signal by the focus position calculator,
• the focus position calculator sets, as the focus position of the objective optical system in the tomographic image corresponding to the reflected light intensity distribution, a position where a distance to the first principal surface in the optical axis direction in the reflected light intensity distribution obtained from the interference signal obtained with the focus position adjustment amount of the objective optical system set at a third adjustment amount, the second adjustment amount being between the first adjustment amount and the third adjustment amount, is a second distance expressed by a sum of a value obtained by multiplying a difference between the third adjustment amount and the second adjustment amount by a square of a refractive index of the medium and the first distance.