I like this response. From:
“The event horizon of the Medieval Milieu has been badly crossed with this theory; a corpse hanging in the sun for several days at about a 15 feet distance from an optical quality quartz crystal inserted into the pinhole of a giant Camera Obscura, while inside the Camera, again at a fifteen feet distance, a 14 feet long cloth hangs evenly covered with silver nitrate. Later on, to fix the image, the cloth is washed in a 5% diluted solution of ammonia or urine. Bingo. The first photo, a giant one at that, has been made, after the corpse has been turned upside down for a repeated performance for another seven days or so, the first position matching the second one perfectly.
Again, we hear the magic words; I quote “using materials that were available in the 13th century.” Never mind that an analytical and scientific thinking was not developed yet in the 13th century capable of bringing together the following process: a camera obscura not in use in the 13th century, the classics not yet translated, chemistry not yet invented, yet knowing the exact chemical properties of silver nitrate, knowing its light sensitive properties, without any knowledge of optics or the properties of light employing a bi-convex, finely ground quartz lens, knowing the properties of UV radiation before electromagnetism was known at all, knowing how to stabilize the image by ammonia or knowing the chemical properties of urine. Knowing that some day, from the negative through photography a positive image will be achieved. But how come, that not knowing the most evident fact, that corpses do not maintain rigor mortis or that they cannot hang for 14 days in the sun, or else you would not care to see what the camera obscura would bring in onto your canvas.”