Wilco WLS-LFS20.0MM SETC20.0, WIlco 20mm Lens Focusing Shim Black Anodized Spacers, Shims, Extenders, differences and similarities: Lens spacers are used to increase the magnification or shorten the working distance of fixed focal length lenses by increasing the image distance. They also reduce the total track length of the system. However, they may degrade the optical performance and limit the working distance range of the lens. Shims are thin spacers used to precisely control the working distance and image quality of fixed magnification lenses such as telecentric lenses. They can compensate for variations in flange distance or chromatic focal shift. They are often included with many telecentric lenses. Focal length extenders are negative elements that change the focal length of a lens by a multiplicative factor. They can reduce the field of view without changing the working distance range. However, they may introduce additional optical aberrations and reduce the light throughput of the lens.
