Below is a link to an interview with David Hockney, where he explains and demonstrates the use of camera obscuras and camera lucidas in the artwork of the Old Masters chronicled in his book “Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters”. What do you think about this, are you convinced and what does this mean for us today?

http://www.youtube.com/watch?v=GUs7QqJ87Mc