Depth of field
The distance between the closest and farthest objects in focus within a scene as viewed by a lens at a particular focus and with given settings. The depth of field varies with the focal length of the lens and its f-stop setting or numerical aperture, and the wavelength of light. Depth of fields only a small fraction of a micrometre can be achieved at 546 nm with microscope lenses of N.A. Greater than 0.9.