At first, I found the camera lucida very difficult to use. It doesn’t project a real image of the subject, but an illusion of one in the eye. When you move your head everything moves with it, and the artist must learn to make very quick notations to fix the position of the eyes, nose and mouth to capture ‘a likeness’. It is concentrated work. I persevered and continued to use the method for the rest of the year – learning all the time. I began to take more care with lighting the subject, noticing how a good light makes a big difference when using optics, just like with photography. I also saw how much care other artists – Caravaggio and Velázquez, for example – had taken in lighting their subjects, and how deep their shadows were. Optics need strong lighting, and strong lighting creates deep shadows. I was intrigued and began to scrutinize paintings very carefully.
Secret Knowledge (New and Expanded Edition): Rediscovering the Lost Techniques of the Old Masters
by David Hockney
What is a Camera Lucida?
http://www.cameralucidachambermusic.org/about/optical-devices/
– Encyclopedia Britannica
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The camera lucida was patented in 1807 by William Hyde Wollaston. It may have been described 200 years earlier by Johannes Kepler in his Dioptrice (1611). By the 19th century, Kepler’s description had totally fallen into oblivion, so Wollaston’s claim was not challenged. The term “camera lucida” is Wollaston’s.
– Edmund Hoppe, Geschichte der Optik, Leipzig 1926