The exact point on the optical axis where parallel rays of light converge after being refracted by a convex lens or reflected by a concave mirror. The distance from the lens to this point is the focal length. Properly aligning an optical system requires knowing exactly where this point lands relative to the sensor or target.
Heard on the job
The laser beam needs to hit the exact focal point of the condenser lens to maximize the output intensity.
Also heard as
- principal focus
Related terms
Focal plane
The flat surface perpendicular to the optical axis where an image is sharply formed.
Optical axis
The imaginary straight line passing through the center of curvature of a lens or optical system.
Focus
The point where light rays converge to form a sharp image, or the state of being sharply defined.