Great read, thank you. It goes on ... "The first step was to integrate the equations of light ray trajectories in Schwarzschild space-time and draw the isoradi

Great read, thank you. It goes on ... "The first step was to integrate the equations of light ray trajectories in Schwarzschild space-time and draw the isoradial curves (i.e. at constant radial distance from the black hole) of a thin disk around the black hole, as they would be seen by an observer above the disk's plane" .... "The final black and white "photographic" image was obtained from this pattern. Lacking of an appropriate drawing software, I had to create it by hand. Using numerical data from the computer, I drew directly on negative paper with pen and Indian ink,placing dots more densely where the simulation showed more light (a few thousands dots for the full plate). Next, I took the negative of my negative to get the positive, the black points becoming white and the white background becoming black. The result converged into the pleasantly organic, asymmetrical form reproduced in Figure 8, both visually engaging and scientifically revealing." I am feeling grateful to have started by scientific/engineering computing career one year later than the authors paper in 1980, and as it happens the first year without punched cards at my Univ.