ASTRONOMICAL PHOTOGRAPHY — MEES 211 



covered the dye kryptocyanine^ a carbocyanine from lepidine, with 

 which sensitivity could be obtained up to beyond 8000 A. In 1925 

 H. T. Clarke in our own laboratory found that in some kryptocyanine 

 preparations another dye, which was named neocyanine, was formed, 

 with which the photographic spectrum was extended to 9000 A. The 

 discovery of the tricarbocyanines made it possible to make the tricar- 



\ / 



/C=CH-C 



N N 



Ef Et 



•\ 



C=CH — CH=CH— 0, 

 Et Et 



/ 



C=CH— CH=CH — CH=CH — CH=CH— C 

 / ^+ 



N N 



Ef Et 



\ / 



C==CH — CH=CH— CH=CH— CH=CH— CH=^CH— n 

 / '^+ 



N N' 



Et Et 



/ 



C^CH— CH=CH — CH=CH — CH=CH— CH=CH— CH=CH— C 



/ •^ + 



N N- 



Et Et 



Figure 1. — Cyanine dyes with increasing chain-length structures. 



VISUAL OND PMOTOCnaPHIC SPECTR4 



INfRi-BEO SENSITIZING Bv 

 [ ■ , »ENOCVaNINE 

 llNFRS-RED SENSITIZING Bv 



4ND PENTiCmeOCViNINES 



PHOTOGRAPHIC 1935- 

 k . * 



SENSITIVITY BY N4TUR4L SENSITIVITY OF P4NCHR0MaTIC 1NFR»-RE0 SENSITIZING 



VERY LOW GELATIN SILVER HALIOE IN GELATIN SENSITIZING BY BY OYES 



CONTENT AND BY OYES 



DRESCENT MATERIALS 



Figure 2. — Chart showing progress in the photography of the spectrum. 



bocyanine from lepidine, and it was named xenocyanine. In 1932 it 

 became possible with long exposures to extend the limit of the photo- 

 graphic spectrum to 11,000 A. In 1934 the tetracarbocyanines and 

 pentacarbocyanines were made, with which the spectrum of the sun 



