PLATE 21. 



Comparison of Ordinary and Colour Sensitive Plates. 



BURNET MOTH : Upper-wings, bronze-green with crimson spots; under- 

 wings, crimson with black border. 



COMMON BLUE BUTTERFLY. 



SWALLOW-TAIL : Yellow and black, with blue markings and red "eye" 



on nnder-wings. 



Photographed as described on page 128 with a Goerz 1" anastigmat. 

 The reproductions are reduced from originals of natural size. 



A Ordinary plate. Wratten's "Instantaneous." 



The crimson-black and bronze-green are not differentiated. Blue 

 is given as white. Yellow is too dark. 



B Orlho chromatic plate. Wrat ten's "Allochrome." 



The plate is just sufficiently sensitive to bronze-green to show the 



black spots on the wings in contrast to it. 



Red still appears black, but blue is slightly lower in tone than 



with an ordinary plate and yellow is lighter. 



C Panchromatic plate. Wratten's "Panchromatic." 



All detail is shown; in particular crimson is rendered light in 



accordance with its visual luminosity. 



The yellow is the high light. Blue is still too light, but rather 



darker than in B. 



D Orthochromatic plate and yellow screen. Allochrome plate and 

 "K :J " screen. 



Both Panchromatic and Ortho. plates are proportionately much 

 more sensitive to blue and violet than to other colours, and the best 

 possible colour rendering is only obtained by absorbing all the ultra 

 violet and a suitable proportion of the more actinic rays from the blue 

 end of the spectrum by a yellow screen. Under these conditions a 

 correct rendering of the whole range of colours is obtainable on a 

 Panchromatic plate. 



This figure shows the effect of a K 3 screen on an Ortho. plate. 

 Blue takes its correct grey in the monochrome scale. The green on 

 the upper wings of the Burnet and the yellow are made lighter, but 

 red is not affected. 



Photos. H. L. H. Reproduced from 



Photographic Monthly, July, 1910. [To follow page 168 



