F-Theta lenses – also called scan objectives or flat field objectives – are lens systems often used in scan applications. Located in the beam path after the scan head, they perform various functions.
F-theta objective is normally used together with a galvo-based laser scanner. It has 2 main functions: focus the laser spot and flatten the image field, as shown in the image below. The output beam displacement is equal to f*θ, thus was given the name of f-theta objective. By introducing a specified amount of barrel distortion in a scanning lens, the F-Theta scanning lens becomes an ideal choice for applications that require a flat field on the image plane such as laser scanning, marking, engraving and cutting systems. Depending on the requirements of the application, these diffraction limited lens systems can be optimized to account for wavelength, spot size, and focal length, and distortion is held to less than 0.25% throughout the field of view of the lens.