Exact focusing in microscopic photography is sometimes difficult even at low magnification, because the depth of focus of the focus-detecting system including the human eye is longer than that of the photographing system. We have devised a focus-aid system to improve the focusing accuracy of microscope photography. The standard deviation of the focus position error with the present system is 1.1 μm in 100 trials, which is 1/9 of 9.5μm for manual focusing.
