Recent observational evidence reveals the existence of black holes in the galaxy. Using strong field lensing effect, we find out the expressions of the radius of the photon sphere, the deflection angle, the separation between the first and the other images, the ratio between the flux of the first image as well as the flux coming from all the other images for dilaton–axion black holes and compare the results with Reissner–Nordstrom black holes. We also investigate the variations of primary and secondary image positions as well as their magnifications with respect to the source position for this kind of black holes.
Strong gravitational lensing by Schwarzschild black holes
