Patent ID: 7486329

Claim:
An autofocus system comprising: a focusing state signal output apparatus; a stage on which a sample is set; a focusing part which adjusts a relative distance between the stage and an objective lens; and an external control unit, which is external to the focusing state signal output apparatus, and which controls the focusing part; wherein the focusing state signal output apparatus comprises: an optical detection part which detects light reflected from a sample to carry out photoelectric conversion; a control unit which generates a focusing state signal representing a focused position and a focusing state of the sample based on an electrical signal from the optical detection part; an output part which outputs the focusing state signal to the external control unit; a storage part which stores a threshold value corresponding to a magnification of the objective lens and a type of microscopy of a microscope; wherein the focusing state signal has inverse signs on respective sides of a focused position of the focusing part with respect to the sample, and the focusing state signal shows continuous change of a voltage level crossing a zero at the focused position, and wherein the control unit is configured to transform the focusing state signal to an arbitrary wave form based on waveform setting information from the external control unit, the control unit sets a threshold with respect to the focusing state signal according to at least one of (i) a change in inclination of the focusing state signal and (ii) the magnification of the objective lens and the type of microscopy of the microscope, and the control unit outputs a focusing judgment signal to the external control unit based on a result of a comparison between the focusing state signal and the set threshold.