Here is the artist painting himself in his studio: I don't see anything like lenses, mirrors or other tricks, mostly just brushes, paint, canvas, the artist

Here is the artist painting himself in his studio: I don't see anything like lenses, mirrors or other tricks, mostly just brushes, paint, canvas, the artist and the subject. To be fair, I doubt that Vermeer himself would have wanted to publicize that he was using "crutches" like the techniques described. As others have mentioned, if these techniques were used, they probably would have been treated as trade secrets.