80mm effective focal-length on APS-C cameras, 50mm on full-frame cameras,it's an excellent prime lens for portraits. Large maximum aperture of f/1.8 Silent stepping Motor (Gear-Type STM) realizes quiet AF operation Filter Thread Diameter: 52mm,Minimum Focusing Distance: 17.7" Lens compatible with the Canon EF mount cameras The YONGNUO YN50mm F1.8 lens for EF mount is a peerless standard lens featuring an ultra-large aperture for a narrow depth of field and soft background blur so loved by photographers everywhere.