1. A microscope autofocus system comprising: a microscope including; a stage configured to support a sample; a stage actuator configured to selectively move a stage along at least one axis; an imaging device configured to generate image data representing the sample; and an objective lens between the stage and the imaging device, the objective lens configured to direct an optical image of the sample to the imaging device; and an electronic control unit including a processor, the electronic control unit being configured to: generate a stage actuator control signal to move the stage to a plurality of predetermined positions along a stage range of motion; obtain image data sets representing an image of the sample from the imaging device, the image data sets associated with the predetermined stage positions; apply two 1D spatial size filters to rows and columns of pixels in the obtained images of the image data sets corresponding to the predetermined positions thereby generating a filtered image for each of the obtained images, such that the spatial size filter only allows objects of a size which meet a size criteria of the spatial size filters to remain in the filtered image; determine a focus score for each of the filtered images, the focus score of the filtered images corresponding to a degree of focus in the obtained images; identify a best focus position selected from the stage range of motion by comparing the focus score of each of the filtered images; and control the stage actuator to move the stage to the best focus position.