PHOTOGRAPHY OF AQUATIC ANIMALS. 



47 



it is best to use a lens suitable for instantaneous exposure a lens of a speed not less 

 than f 8. The operator should first select the point from which the picture is to 

 be taken. He should, of course, have the sun at his back or to one side. If possible 

 he should stand on the bank or on some fixed support which extends above the 

 surface of the water. From such a position the camera is at a greater height and 

 may usually be directed at the surface of the water at an angle of about 45 or 

 less from a vertical extending upward from this surface. Rays of light from sub- 

 merged objects striking the surface of the water from below at an angle of 48 35' 

 from a vertical drawn downward (or at a less angle), emerge. They may thus, 

 after refraction, reach the camera as indicated by the line x yf i' in figure 1. Rays 

 which strike the surface of the water from below at an angle of more than 48 35' 

 with the vertical are, on the 

 other hand, reflected at the 

 surface so that they do not 

 emerge and enter the camera 

 but pass down again into the 

 water, as indicated by the 

 line x m n in figure 1 . 



If the operator is unable 

 to find a fixed emergent sup- 

 port for the camera he may 

 make the exposure while 

 standing in the water. The 

 camera may then be held in 

 the hand or may be supported 

 on a tripod which rests on 

 the bottom. As the legs of 

 the tripod are likely to sink 

 into the bottom they should 

 be extended to their full 

 length. Where the bottom 

 is firm an elevated position 

 may be obtained for the 

 camera by using a tripod with legs some 10 feet long, such as dealers sell for use 

 in making pictures of large groups. In such tripods one leg forms a ladder by 

 which the camera may be reached. 



The tripod top should consist of two rectangular wooden pieces, as shown in 

 figure 2 and in section in figure 1. To the lower piece, which has a large circular 

 opening at its center, the legs are attached. The camera is fastened by the tripod 

 screw to the upper piece in such a way that one of the legs projects directly backward 

 instead of directly forward, as is usual. The two pieces are hinged together at one 

 edge, so that they may lie parallel to one another or may be separated like the covers 

 of a book until the upper piece forms an angle of 90 with the lower. A rod is 

 pivoted by one end to the upper piece at the middle of its free edge, so that it swings 

 freely in the vertical plane. This rod passes through a perforated metal block piv- 

 oted by one end at the middle of the free edge of the lower piece so as to swing freely 



FIG. 2. Tripod top by means of which the camera may be inclined at any 

 angle. For explanation see the text. 



