60 



BULLETIN OF THE BUREAU OF FISHERIES. 



A NEW SUBAQUATIC APPARATUS. 



When a camera for subaquatic use is made after the ordinary type the box 

 must be securely closed before submerging it in order to protect the lens and the 

 plates from the action of the water. While the camera is under water it is not 

 possible to remove the plates or plate holder in order to substitute a ground glass 

 for them. It is therefore impossible to focus, and the camera must be adjusted to 

 the desired focus before immersing it. This was the method adopted by Boutan 

 in his third apparatus. It would be possible to construct a camera that might be 

 focused under water by means of a focusing scale such as is provided in those hand 

 cameras arranged to be focused without the use of a ground glass, the operator 

 estimating the distance of the object and then setting the camera for a corresponding 



division on the focusing scale. This 

 method is of value for more distant ob- 

 jects and with rather slow lenses of 

 great focal depth. When very rapid 

 lenses are focused on near objects only 

 those objects are in focus that lie nearly 

 in one plane. Thus a very accurate ad- 

 justment of the camera is necessary in 

 order to bring any near obj ect into sharp 

 focus, and this is not possible when the 

 distance of the obj ect must be estimated 

 and the focusing accomplished by means 

 of a scale. In subaquatic photography 

 the objects to be photographed are all 

 near and if instantaneous work is to be 

 done the lens must be very rapid. It 

 is therefore important to be able to focus 

 accurately on the ground glass under 

 water, and this might be accomplished 

 by using two identical cameras (twin 

 camera) united so as to form one instru- 

 ment. One of these contains the plates 

 and has a lens provided with a shutter. 

 The other camera carries the ground glass. The same focusing mechanism operates 

 both cameras, so that when a sharp image is formed on the ground glass of the one an 

 identical image strikes the sensitive plate in the other when the shutter is operated. 

 One of the cameras serves merely as a focusing finder of full size. A camera of this 

 type properly constructed of metal could undoubtedly be used successfully under water, 

 though it has the disadvantage of being unnecessarily cumbersome and expensive. 



THE CAMERA. 



All of the advantages of the twin camera are to be had by using a reflecting 

 camera, which is at the same time both lighter and less expensive. The principle 

 of the reflecting camera is shown in figure 9, which represents diagrammatically 



FIG. 9. A reflecting camera shown in section, with magazine 

 plate holder attached, gl, ground glass; h h', hood; Z,lens; m, 

 mirror in position during focusing; m', mirror, showing position 

 during exposure; p, sensitive plate; r and r', rollers of focal 

 plane shutter; s, the shutter; si, slot in shutter; x, hinge on 

 which mirror turns; y y y', ray of light traversing the lens and 

 reflected from the mirror to the ground glass. 



