You're going to be hearing a lot about the recently "authenticated" painting by Leonardo da Vinci called "Salvator Mundi", because it will be auctioned at Christie's in November 2017 for hundreds of millions of dollars. https://en.wikipedia.org/wiki/Salvator_Mundi_(Leonardo_da_Vinci) The Wikipedia link to a jpeg of the picture itself: https://upload.wikimedia.org/wikipedia/commons/1/1f/Leonardo_da_Vinci_or_Bol... Here's a major problem IMHO with this painting: The (supposedly rock crystal) "orb" should distort the image behind it far more than it does in this painting, and da Vinci *would have known this*, as he did a lot of experiments with lenses and mirrors, designed lens and mirror grinding apparati, knew about the camera obscura, and supposedly invented the first *contact lens*! (I myself own a solid glass sphere much like the one in the painting, and I can vouch for the substantial distortion it makes when you view objects through it.) Da Vinci was famous for constantly updating his paintings (many of which were never finished) when he learned something new that would change how the painting should look. E.g., Isaacson's new biography of da Vinci mentions the fact that da Vinci updated the neck area of a painting after his human dissections showed that the neck muscle was different from what he had previously assumed. There are several possible explanations for the lack of orb distortion in the painting being auctioned by Christie's: * the particular area of the painting has undergone *bad conservation* by conservators who demonstrated their profound ignorance of optics when "repairing" the painting; * the orb isn't a sphere at all, but a thinner *lens*; but why in the world would da Vinci replace the standard spherical orb symbol with a lens? Possibly as an inside joke re his use of lenses to get his images right (see artist David Hockney's theories about these Renaissance painters and their optical devices)? https://en.wikipedia.org/wiki/Hockney%E2%80%93Falco_thesis * the orb isn't solid at all, but more like a transparent glass Christmas tree ornament, so it wouldn't distort the image underneath nearly as much as a solid rock crystal. Glass blowers could have made such a hollow orb for da Vinci, and da Vinci was known to have experimented with hollow glass "lenses" which he filled with water & other liquids for experimentation. Isaacson and the "experts" at Christie's claim that da Vinci went to a lot of trouble to paint "inclusions" (small bubbles) in the supposedly rock crystal material. They even claim that the crystal could be doubly refracting, and that da Vinci captured that. Then why in the world would da Vinci screw up the even more obvious feature -- the distortion caused by this supposedly solid crystal object? Perhaps there is a simpler explanation: the little dots aren't *inclusions* at all, but *specular reflections* of da Vinci's lights used to illuminate the orb model while it was being painted? Specular highlights would also be consistent with a hollow glass sphere or a lens. BTW, the modern computer graphics technique of "ray tracing", which is the computer implementation of "geometric optics", is required to properly handle refractive objects -- e.g., lenses, orbs. Ray tracing is quite computationally intensive, requiring large supercomputers to implement; most of the latest Hollywood animated features incorporate the sophisticated effects obtained from ray tracing, although they don't want to go so far as to make the animations look "too good", else people will forget that they *are* animations. Some of the later Dutch painters loved to show off their incredible skill by including such distorted images from reflections in curved objects and through lenses. There was a Scientific American article from 30+ years ago that discussed some of these effects. https://en.wikipedia.org/wiki/Ray_tracing_(graphics) https://en.wikipedia.org/wiki/Geometrical_optics If one has a good enough model of the image behind such an orb, it should be possible to *invert* the ray tracing computation to reveal the actual shape of the lens/orb which is providing the distortion.