10 THE PHOTOGRAPHIC IMAGE, BROCK 
In general, square waves cannot be reproduced near the upper frequency limit of the 
system, and if passed through it near that frequency they will emerge as sine waves. In 
the T.V. example quoted, the viewing distance necessary to “lose” the lines limits the 
perception of detail along any line and there is no point in transmitting frequencies much 
higher than 2 Mc/s. A 3 Mce/s bandwidth in fact gives very good results on a 400 lines 
system. This system could be tested quite well for "sine wave response" at its limit by 
using sharp-edged 2 Mc/s lines, because the harmonics would be lost. (The harmonics 
soon become negligible, because the 3rd has only !/4 of the fundamental amplitude and 
so on.) 
2.4. Application to photography. 
24.1. General 
What can be gained by applying these ideas photographie problems? Can they help 
us to obtain a better understanding of photographic imagery, better test methods, better 
  
  
  
  
  
  
  
1.0 [m Te cce meu eve pee og 
| | | | | | 
| | | 
| | | | 
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I | | | | 
| | | | | | | | | | 
96 H——"-—<—}k"" Hire 
| IST HARMONIC | | | | | | | 
| | (fundamental) | | 
Sa PEN | i bf 
s | d ! | | | | 
| § th Y | | | | 
3 | | | 
id eb Lt Ed bod 
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AN | 
a CEN | | | | | 
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I [ | 11th | | | | 
| qath | | | | | | | 
= Gd et . el | 
| | | SUM OF HARMONICS 1 TO 15 
| | | ‘ | | 
| | | | | | 
06 P v Ln 4 EN A AA e d | = 1 
| | | | 
  
—10 EE as A du xe d. lon { : | i Em ] 
o? 30* |. 60? 90° 420° 150° 180° 210° 240% 270° 300" 330 369 
PHASE OF FUNDAMENTAL WAVE 
Fig. b. Showing the analysis of a square wave into fundamental and series of 
odd-numbered harmonics. 
equipment and materials? The short answers to these questions appear to be: “Yes”, 
“Possibly”, and “Probably not, at least not directly”. 
Various terms have been used to describe the ratio of modulations in object and 
image, perhaps most common being “Frequency Response”, but it is now preferred to 
use “Contrast Transmission”, abbreviated to “CT” as by Ingelstam. This gives a simple 
and direct expression to the effect of the system on the image it transmits. 
At present we describe the behaviour of the camera, considered as a contrast-transfer 
system, in terms of emulsion characteristic and optical veiling glare for large areas, and 
resolving-power for small details. That is to say, we can give numerical expression to 
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