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 f4. 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, J 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 
