Nail clipper allows for removal of any excess nail that is jagged or has been missed. Nail clippers occasionally come with a pocket knife or a nail catcher; the multi-purpose nail clipper was invented by Hungarian inventor David Gestetner. The nail clipper consists of a head which may be concave or convex. Specialized nail clippers which have convex clipping ends are intended for trimming toenails, while concave clipping ends are for fingernails. The cutting head may be manufactured to be parallel or perpendicular to the principal axis of the cutter. Cutting heads which are parallel to the principal axis are made to
Lens (optics) object off the optical axis of the lens is imaged, where rays pass through the lens at an angle to the axis θ. Rays that pass through the centre of a lens of focal length "f" are focused at a point with distance from the axis. Rays passing through the outer margins of the lens are focused at different points, either further from the axis (positive coma) or closer to the axis (negative coma). In general, a bundle of parallel rays passing through the lens at a fixed distance from the centre of the lens are focused to a ring-shaped