BRIEF HISTORICAL SUMMARY 



675 



While mirrors had been used in the camera obscura for changing the position 

 or causing the images to appear erect, so far as known at present, no one used a 

 projection lens in the aperture of the dark room until 1568. In that year was 

 published the work on perspective by Daniel Barbaro, and on p. 192, Ch. V, he 

 directs that to make the image more brilliant, a convex spectacle glass be put 

 in the aperture, and that a white paper screen be moved back and forth until 

 the picture shows most clearly, then it can be traced. From this time onward 

 a projection objective has always been used, except for experiments, such as 

 with pin-hole photographic cameras, etc. 



In the camera obscura considered above, the observers were in the room 

 where the picture was formed. For a small, movable camera, something like 

 the photographic cameras of the present, where the observer is outside the 

 camera box, the first description found by us is the one of Robert Boyle, and 

 dates from 1669. He called it a "A Portable Darkened Room," and says that 

 it had already been exhibited to many friends several years before the paper 

 was written. 



FIG. 403. WALGENSTEN'S MAGIC LANTERN (1665). 

 (From Milliet de Chales, Mundus s. Cursus Mathematicus, 1674, vol. ii, p. 666) 



Here is a naked light with a reflector behind it. There is no condenser. 

 The object is put in the proper inverted position before the objective, and the 

 image appears erect and enlarged on the screen. 



III. PROJECTION INSTRUMENTS 



The third form of projection apparatus consists of a relatively small instru- 

 ment in which a small object is brilliantly illuminated, and the light from it 

 extends out through a projection lens or objective and forms a relatively large 

 image on a white wall or screen in a dark place. 



The third form is the converse or conjugate so to speak of the camera obscura 

 where the object is large and the image small. 



