The Lee Seven5 ND 4 stop ProGlass IRND is a 75x90mm neutral density filter manufactured from 2mm thick optically flat glass. Originally developed for the movie industry, to meet the exacting requirements of leading cinematographers the ProGlass IR filters have virtually no colour shift and extremely accurate stop values. They also block both ultraviolet and infrared pollution, creating accurate, crisp and punchy images. To accompany the filters, a Lee exposure app is available free to download for Apple and Android devices. ProGlass IR ND filters come in 0.6ND (2-stop), 0.9ND (3-stop), 1.2ND (4-stop), 1.8ND (6-stop), 3ND (10-stop) and 4.5ND (15-stop) versions, to cover every photographic need, from subtle alterations up to ultra-long exposures.