Squash preparation of stained onion root tip cells showing various stages of mitosis. Differential interference contrast optics on a Leica microscope, Image taken with the X40 objective lens. Depth of focus is extremely shallow (just a few microns). Differential interference contrast results in an optical slice horizontally through the specimen providing maximum possible resolution at this magnification and good contrast. Chromatic abberation is inevitable in light microscopy, but has been kept to a minimum in this image.