188 MARVELS OF FISH LIFE 



already illustrated how these photographs can be 

 obtained in the pond. 



Now let us turn our attention to the camera, lenses, 

 plates and exposures. For general use I would recom- 

 mend a reflex camera, taking a five by four inch plate, 

 with a lens of eight or nine inches focal length, and work- 

 ing at/4. The fastest backed orthochromatic plates com- 

 patible with easy manipulation must be used. Several 

 factors affect exposure in fish photography beyond those 

 that have to be taken into account in ordinary photo- 

 graphy. For example, some fish invariably move much 

 faster than others ; and, again, the water in which the 

 fish is photographed varies considerably in clearness. 

 As a general rule, I would recommend the photographer 

 to decide what would be the correct exposure for any 

 particular fish if placed in front of the tank. In fresh 

 water 25 per cent, and in sea water 50 per cent, increased 

 exposure should be allowed for every six inches of 

 water through which the photograph is taken. Expo- 

 sures in the pond vary according to the depth at which 

 the fish is down in the water. 



Now we come to the photography of smaller forms of 

 fish life. 



At Port Erin I took the photographs of the trans- 

 formation of the plaice on the plates facing p. 114 with an 

 improvised apparatus. Provided that the illumination is 

 sufficiently good, and that the lenses are suitable for the 

 work, it is possible to get quite as satisfactory a result 

 with an improvised apparatus as with a more elaborate 



