12 NATURE AND THE CAMERA 



halation plates are those which prevent the blurring 

 around the strongly lighted parts; as, for instance, a 

 window from the inside of a room would be a blur 

 with an ordinary plate, while with the backed or 

 nonhalation plate the edges would be well defined. 

 Ordinary plates will do well enough for snap-shot 

 work, provided they are fast enough. It is well to 

 remember that the more rapid the plate is the less 

 latitude you have in exposure; in other words, the 

 more rapid the plate the more nearly correct should 

 the exposure be. For long trips where weight has 

 to be considered, cut films are a good substitute for 

 plates. These, as made by both Carbut and Seed, 

 are really excellent, comparing favourably with glass 

 plates. Their keeping qualities also are good. In 

 using ray-filters and the best of them are of col- 

 oured glass always use an isochromatic plate ; the 

 exposure is of course increased according to the 

 density of the colour-screen. Over-exposure is a 

 common error when the ray-filter is used. With 

 a light-coloured glass and isochromatic plates the 

 exposure is increased about four times with instan- 

 taneous plates, while with slow plates it is much 

 less, as the slow isochromatic plates are so much 

 more sensitive to the yellow light. 



