Fixed Focal Length Lens Extenders can be used to increase an imaging lens’ focal length by adding a negative focal length doublet lens to the camera end of an optical system. These extenders can decrease the field of view while maintaining the original working distance specifications. For instance, increasing the focal length by 2 decreases the field of view by the same factor. Therefore, the 2X extender converts a 25mm FL lens to a 50mm FL lens. Fixed Focal Length Lens Extenders have threads to connect between the camera and lens. They are specifically designed for compatibility with C-Mount video lenses.