All-encompassing 180° fisheye coverage produces a circular image on the film; everything in front of the camera is included in the picture. Bright f/2.8 aperture makes it easy to view and focus, even in dim light. Close focusing down to 0.3m (1ft). Rapid changing of filters- 5 filters (skylight, medium yellow, dark yellow, orange, and red) are built into a revolving turret inside the lens. Truly creative pictorial effects impossible with any other type of lens; extreme barrel distortion makes lines bow in, while exaggerated perspective makes objects close to the lens very large indeed. Used in science and industry for weather and cloud observation, astronomical studies, surveillance work, and for photographing inside confined areas, such as airplane cockpits, tunnels, pipelines, heating or air conditioning conduits, etc.Lens construction- 10 elements in 8 groups, Distance scale- graduate in metres and feet from 0.3m (1ft.) to infinity (∞), Weight- 1100g, Lens case- CL-11 hard leatherette, Usable teleconverter- TC-201 or TC-14A.