338 T. V. Shcherbakova 



graphy in a well, the clay suspension or turbid drilling fluid must be re- 

 placed by clear water. 



In well cameras the viewing window is put as close as possible to the wall 

 of the well, but for one reason or another (constructional shortcomings of 

 the instrument, unevenness of the walls of the well) the distance from the 

 viewing window to the rock in many cases will be of the order 10-20 mm. 

 Hence it follows that, to provide for photography of the well, the liquid 

 filling it must have a turbidity not greater than 4 per cent. If the well is 

 filled with ordinary drilling fluid of specific gravity 1.2, then before photo- 

 graphy this clay suspension must be diluted to more than ten times with 

 clean water*. 



In photography the necessity to have the barrel of the well filled with 

 comparatively clear water is a real disadvantage of the method, but this 

 does not exclude its application where it is necessary to study the geological 

 section of a well. 



SOME PROBLEMS OF PHOTOGRAPHING ROCK SAMPLES 



In order to investigate some problems connected with photographing 

 rocks along the walls of a well, photography of some samples was carried 

 out at the surface. 



1. Light of different spectral composition has different absorptive and 

 reflective capacity. In connection with this photographs of rock samples 

 will differ somewhat, depending on the light in which the photography 

 takes place. To find out the difference in the nature of photographs taken 

 in different light, photographs of rock samples were taken in ordinary light, 

 infra-red and ultra-violet rays. 



Samples of sandstones, clays, siltstones, gypsum, dolomite and anhydrite 

 were photographed; some of the samples which were photographed in ultra- 

 violet illumination contained petroleum. 



The source of infra-red rays in photographing the rock samples was an 

 ordinary 500 W incandescent lamp with a dark -red filter. The films used 

 in this case were two types, produced at the Scientific Research Institute 

 for Cinematography and Photography, of infra-red film sensitive respectively 

 to rays of wavelengths 840 and 960 m^. 



As a result of comparing j^hotographs taken with ilhnnination by ordinary 

 and infra-red rays, the following was established. 



* Actually, depending on the method of illuminating the fluid, considerably greater 

 dilution may be required. 



