Yes, the Dave Hockney book is good on this, but keep in mind, he isn’t saying the Renaissance painters used the lenses, rather the change came right after that with artists such as Caravagio and on, with the influence of the lense technology the dutch painters were developing.
Its easy to see the difference once it is pointed out, and you have an understanding of how the systems available were used.
Rubens, Michelangelo and Rembrandt were draftsmen, and it shows, you can see them feeling for the final lines even in their paintings.
But soon after everyone can produce paintings with a realism that seems beyond what anyone could learn drawing the figure for 4 years in even the best art schools.
Ever wonder why Ingres little portrait drawings were all the same size and look like tracings with no mistakes? Becuase that is what they were.
Don’t get me wrong, I am not criticising here. It is the same today for artists. You may feel that your struggle to develop your art using traditional methods is the best for philosophical reasons, but the kid down the block just bought a quad from BOXX with 64 bit software and he’s going to your clients with faster turn-around and higher quality than you can produce with your 32 bit system. You know what your going to do if your going to stay in the game.