confocal

a microscope that allows the observer to visualize objects in a single plane of focus, thereby creating a sharper image (usually the objects are fluorescent molecules); a refinement of this microscope uses optic sectioning and a computer to record serial sections. This permits three-dimensional reconstruction.

Having the same focus. Example: in a slit-lamp, the microscope and the illumination system have the same focus, i.e. they are confocal. See confocal microscope; confocal scanning laser ophthalmoscope.