 They admired it very much and could hardly be convinced by Della Porta's explanations that what they had seen was really an optical trick.The earliest use of the term "camera obscura" is found in the 1604 book "Ad Vitellionem Paralipomena" by German mathematician, astronomer, and astrologer Johannes Kepler.Kepler discovered the working of the camera obscura by recreating its principle with a book replacing a shining body and sending threads from its edges through a many-cornered aperture in a table onto the floor where the threads recreated the shape of the book.