Null Geodesics and Strong Field Gravitational Lensing in a String Cloud Background

Figure 4

Basic lens formalism: position of source, image, lens, and observer are represented by , and . The distance between lens-source, lens-observer, and source-observer are denoted by , , and , respectively. The line connecting and is called optical axis of the lens geometry. The angle is the location of the source , while the position of image is denoted by angle with respect to optical axis. The impact parameter is given by [36].