Mr. A. Claudet on the Optics of Photography. 217 



but still sufficiently defined to show the exact form and size of 

 the pin. 



Now what has been done for the two extreme segments of the 

 focimeter Nos. 1 and 8, can consecutively be done for the inter- 

 mediate segments Nos. 2, 3, 4, 5, 6, 7, and 8; and in fact it is un- 

 avoidably done during the movement of the plate from No. 1 to 

 No. 8 '; and the result is that every segment has the image of any 

 small spot delineated upon it as if that spot was seen through a 

 thin vapour. 



This being well understood, let us apply the same mode of 

 operating to the taking of a portrait; and while the person 

 is sitting, let us move the frame holding the plate from the 

 point of the focus of the nose to the focus of the furthest point 

 of the figure. It is evident that during the movement of the 

 plate the various planes of the figure will have been consecutively 

 in focus and out of focus during one part of the exposure, and 

 all in the same degree. Thus we have by a very simple contri- 

 vance found the means to realize the wish of true artists, viz. to 

 take a photographic portrait without hard lines, but with the 

 light and shades blended in the most artistic harmony. 



We now arrive at the most important part of the discovery. 

 The result may be obtained in greater perfection without having 

 to move the frame holding the plate in order to adapt it consecu- 

 tively to the focus of each of the planes of the figure. In moving 

 the frame, it is evident that in one direction we increase, and in 

 the other we reduce the size of those parts of the image which 

 are consecutively brought into focus. The result is to exhibit 

 more conspicuously than when these parts were out of focus the 

 exaggeration of perspective which is inherent to all photographic 

 representations taken by lenses not very distant from the figure — 

 an exaggeration, I may remark, so disagreeably apparent in all 

 large portraits taken by too short-focus lenses. To obviate this 

 increase or reduction of the size of the image of the various 

 planes of the figure, it would be necessary, if this were practi- 

 cable, during the operation to change the lens and rapidly to 

 substitute another having a focus appropriate to the distance of 

 the new plane without altering the distance of the plate, so that 

 the plate should not have to be moved forward or backward for the 

 adaptation of the various foci according to each distance of plane. 



It happens fortunately that this change of foci may be effected 

 with the same object-glass when that object-glass is a double 

 combination of lenses. The focus and power of such double 

 combination being the result of the distance which separates 

 the two lenses, it may be increased or reduced merely by alter- 

 ing that distance. Now if during the operation we bring nearer 

 or further the two lenses, by this simple means we adapt the 



