444 



TYLER AND PREISENDOBFER 



[chap. 8 



ACHROMATIC 

 -COLLIMATING LENSES 



EXIT SLIT 

 PHOTOTUBE CATHODE 



OPTICAL SYSTEM 

 Fig. 25. Arrangement of the optics in the Hubbard submersible monochromator. The exit- 

 sHt mirror covers the upper half of the collimating lens so that the incoming flux 

 passes under it to the prism. Irradiance is measured by utilizing an irradiance col- 

 lector in front of the collimating lens on the left. 



