I mentioned in a recent post that I had posted a response to Hockney's book on my website. I would like to direct attention to the two articles at
www.kirkrichards.com/articles.htm
concerning Hockney's theory.
One article there deals with Hockney's total misunderstanding of the artists' motivation and uses quotes from the artists themselves to demonstrate the error of his thesis, and also describes the standard requirements of students who competed for the prestigious "Prix de Rome." Ingres and others who competed and won did so under the careful scrutiny of judges and officials and no optical aids of any sort were permitted.
The other article by Gregg Kreutz takes Hockney's 7 main "proofs" and responds to them point by point.
Take a look.
Best,
Kirk