The Linhof Super Fresnel Screen (lens) is an accessory for a groundglass focusing screen. It helps "even-out" the brightness of the groundglass image and make the image appear brighter. The effect is more noticeable with wide angle lenses. Fresnel lenses are essential when using reflex housings.
Note: Mandatory for accurate exposure readings with the Linhof Focusing/Metering Bellows accessory.