The Fisheye-Nikkor actually sees a full 180 degree hemisphere: everything in front, above, below, to either side - all around. And it records this hemisphere on the film as a circular image 23mm in diameter. There is no need nor provision for focusing because of the extreme depth-of-field of the lens (20 inches to infinity at full aperture). And because of its extreme angle, it cannot be used with a lens hood. The Fisheye-Nikkor has 6 built-in filters; Skylight L1A, Medium Yellow, Deep Yellow, Orange, Red and Light Green. weight: 12 1/4oz.