The Samyang Optics 10mm T3.1 VDSLR ED AS NCS CS II is an ultra-wide-angle lens with manual focus designed for APS-C sensors. It has been specifically developed for professional film and video work, featuring a focus gear for follow-focus systems. With the decoupled aperture gear, you can change the aperture quietly and smoothly. The T-number, which determines the actual amount of light transmission, and the distance scales are marked on both sides of the lens for very precise filming. The lens operates with a manual aperture system with a low T-number, allowing for natural shooting under various lighting conditions.