The latest optical processing technologies of HOYA PROND EX filters combined with ultra-clear mineral glass ensure exceptional optical performance: ? contrast and colours respected ? stitched images without deformation The exclusive HOYA ring fitted with PROND EX filters ensures perfect sealing to stray light inputs that can be used for long exposure. The exclusive HOYA 2nd generation Accu-ND optical processing enables equal reduction in both visible and infrared. PROND EX 500: Optical density 2.7 Transmittance T%: 0.2% Reduction: 9 diaphs