Our fixed focal length lenses incorporate focusing mechanisms to allow working distances from infinity, where they are designed and optimized, to as close as 100mm. At such a long working distance, most lenses are difficult to fix in bench top applications, and provide fields of view larger than required. Spacers address these issues by reducing minimum working distance and by increasing magnification which decreases field of view. The diagram below illustrates what happens when a spacer element is placed between the camera and lens. The image distance increases, which shortens the object distance according to the magnification formula. Therefore, the magnification of the system increases and field of view decreases as more spacers are inserted (i.e. image distance increases).
Our C-Mount Extender Kit provides spacers for decreasing field of view and reducing working distances of standard fixed focal length lenses. The C-Mount Extender Kit includes 0.5mm, 1mm, (2) 5mm, 10mm, 15mm, and 40mm spacers. Decreasing working distance by adding spacers forces the lens to focus at distances that are generally outside their designed working distance, which can cause increased distortion, chromatic and spherical aberrations, reduced depth of field, illumination non-uniformity, and decreased light-gathering ability. C-Mount Extension Tubes and Brass Spacers are also sold separately.