Mr. A. Claudet on the Optics of Photography. 219 



images superposed one upon another. For this reason nobody 

 would ever have thought of proposing to employ a lens which, 

 moving during the exposure, would adapt itself consecutively to 

 the foci of all the other planes of the image. But from the fact 

 that the eye can easily and usefully alter its focus according to the 

 distance of the plane it wants to examine, and unconsciously dis- 

 card the image of the other planes while they are out of focus, it is 

 possible to learn what may be a very useful modification of the arti- 

 ficial optical instrument called the camera obscura. If we cannot 

 discard the superposed images out of focus, and see only among 

 them the one in focus,it happens fortunately that the image in focus 

 is stronger, better defined, and consequently more conspicuous 

 than all the others. If we cannot discard entirely the images out 

 of focus, they at all events appear only like a number of blended 

 shades of the principal image. Therefore in this process for 

 changing the power and the focus of the double combination of 

 lenses according to the distance of the various planes, we do no- 

 thing but imitate one of the most beautiful and indispensable of 

 natural contrivances, by which the eye is so wonderfully well 

 calculated to perform all the exigencies of perfect vision, and is 

 one of the most marvellous and splendid works of the Creator. 



This new plan of operating not requiring a longer sitting than 

 the old process, the interposition of the usual diaphragms will, 

 by cutting off the oblique rays, increase the definition of the 

 compound image. It follows that, as much as the intensity of 

 light will allow, the smaller the aperture of the diaphragm is, 

 the more perfect will be the result. 



One of the great advantages of the method I have described is 

 that the various planes of the figure are represented with the 

 same intensity of light, which is not the case when the rays are 

 more condensed on the plane of exact focus than on the other 

 planes. For it is obvious that the difference of intensities of 

 light on the various planes produces an unnatural effect, and de- 

 stroys so far the harmony of the picture. 



I have felt justified in bringing this matter before the Associa- 

 tion, from the confident hope that, by the examination of scien- 

 tific photographers, a new era may henceforth begin in the art of 

 photography. If the plan I propose is in its present state defi- 

 cient in many practical points, as must be the case in almost all 

 new inventions, I am sure that, with the cooperation of so many 

 ingenious aud active minds which are constantly engaged in the 

 task of progress, the science of optics will be able to supply 

 photographers with a camera obscura which in its working will 

 approach as near as an artificial instrument can approach the 

 beautiful instrument which gives to man the most. perfect per- 

 ception of all the wonders and beauties of nature. 



