n. ~ 1. The sharpness of an image created by an optical system. - 2. The plane where an optical system causes light rays parallel to the system's axis to converge. - 3. A concentration.
- v. ~ 4. To adjust an optical system so that the image is sharp.
Focus1 is perceived in terms of sharp, distinct lines and high contrast. Focus is relative to the optical system; distortion in the system may degrade focus.