Table 7 EQ. 16 
Depth, Depth, Error, 
meters meters meters 
  
1,000 
2,000 
3, 000 
4,000 
5,000 
6,000 
7,000 
999,14 
1,998.3 
2,999.7 
319997 
9,000.5 
6,002,1 
7,002.8 
-0.6 
-l.7 
-0.3 
-0.3 
0.5 
2.1 
2.8 
Table 9. Error of Eq. 16 
The high water pressures listed in Table 3 of Ref. 3 were 
produced in the laboratory of the National Bureau of Standards. 
Determine by Eq. 16 the approximate equivalent depth of pure 
water for a pressure of 5,064 decibars. 
z . (2.0395) (5,06) 
- (0.99987+1.02385) 
Z = 5,103 meters or 16,742 feet. 
As previously mentioned, modification of Eq. 16 is required 
for increased operational accuracy and effectiveness. 
Eq. 17 is based on the work conducted by Washer and Gardner 
(Ref. 8) at the National Bureau of Standards on depth of 
focus of lenses. 
CN 
RE > A; 2, 
lens resolution in cycles per mm 
constant of 1.25 for high contrast target (100:1) 
and 0.625 for low contrast target (1.611) 
lens f-number 
e change in back focal distance of lens in mm. 
The equation to determine the change in the back focal dis- 
tance of an underwater lens owing to a change in the water 
refractive index and the nodal object distance is presented 
as follows from Tech Memo No. 13, Supplement No. 2, dated 10 
July 1975: 
  
Ob = (Y om - Eq. 18