What a pearl!

[Bongo]

the device is two mirrors. A big mirror reflects the image to a smaller mirror (like a dental mirror) held at a 45 angle over the canvas Vermer could then recreate the image -without tracing - and match the hues and values exactly. We see Vermeer's Music Lesson being reproduced live on camera by a TIm a less-than-novice painter. Tim also built a recreation of the set, gound the lense, an milled the paints!

 

[Artyczar]

I watched Tim Vermeer first and was convinced the device was used by artists in the past.