342 



T. V. Shchebbakova 



0^\ing to constructional considerations it was not possible to provide oblique 

 illumination to the wall of the well. The rock is transmitted to the cameira 

 of the upper part of the instrument through the same window. 



The position of the mirror can be varied within certain limits; being 

 chosen so that light flashes, reflected from various parts of the camera, do 

 not fall on to the photographic film. 



The light source and mirror are put into a glass cylinder; in the casing 

 opposite the mirror there is an opening 5.4 cm x7.8 cm forming the viewing 

 window. The lower part of the instrument is filled "with distilled water; 

 a pressure compensator serves to equalize the pressures outside and inside 

 the chamber. The lower part of the instrument is separated from the upper 

 part by thick glass; hermetic sealing is provided by rubber packing. 



The objective lens and film-winding mechanism, are situated in the upper 

 part. An Industar-22 lens (focal length 52.4 mm, aperture 1:3.5) was chosen 

 as the objective lens. 



Fig. 8. Path of rays in well camera. 1 — driUing fluid; 2 — viewing glass {n = 1.46); 



3 — ^water (re = 1.33) filling part of instrument; 4 — ^protective glass (re = 1.5); 5 — air 



(re = 1) ; HH' — principal planes of objective ; 00' — axis of optical system ; F^^ , F^ — 



forward and rear foci of objective. 



The instrument is enclosed in steel casing; in the lower part the casing 

 of the compensator with a head for the load is screwed in, and above it 

 there is a light bridge with the three lamp leads. On the instrument are 

 fixed springs which press the side of the instrument on which the viewing 

 window is located to the wall of the well. 



The instrument is lowered on a three -strand cable. One strand carries 

 the supply for the electric motor of the film-winding mechanism, another 

 carries the supply to the series-connected lamps of the light source, and the 

 third strand is common to both, circuits. The contact located on the film- 

 winding mechanism switches a certain resistance into parallel with the 

 electric motor when the film is wound -on the length of one frame. The 

 winding-on of the film is controlled by the increase in current intensity 

 associated with this switching. 



