Patent ID: 7851735

Claim:
A microscope having an automatic focusing device for adjusting a relative distance between a microscopic objective and a testing subject due to a different focus length therebetween, comprising: a beam splitter set having a beam splitter; a laser emitting device disposed at a first side of the beam splitter set for providing a laser beam to the beam splitter set; an image detector; an eye piece; the microscopic objective disposed between the beam splitter of the beam splitter set and the testing subject, allowing an image of the testing subject to pass through and enter the image detector via the eye piece, focusing the laser beam from the beam splitter onto the testing subject, and allowing a reflected beam from the testing subject to pass through and enter the beam splitter set; a lens set disposed at a second side of the beam splitter set and opposing to the testing subject positioned at a third side of the beam splitter set for refracting the reflected beam from the testing subject for generating a light spot; and a photo detecting device disposed with respect to the lens set for receiving the light spot and generating a driving signal, wherein the photo detecting device determines a defocus distance ranging from 10 to 100 micrometers based upon an astigmatism shape of the light spot, and generates the driving signal based upon the defocus distance.