In
optics,
defocus is the
aberration in which an image is simply out of
focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a
translation along the
optical axis away from the plane or surface of best focus. In general, defocus reduces the
sharpness and
contrast of the
image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality.