Commission I Presented paper 
Dodging, a Non-Linear Element in the Contrast Transfer of the 
Photographic System 
by S. A. HEMPENIUS 
LT.C., Delft *). 
In aerial photography, dodging printers have found a widespread application. A sound 
basis for the understanding of their function is the Contrast Transfer Theory. 
The general situation in the field of Contrast Transfer is that the theory is ahead 
of the experiments. In the case of the dodging printers, Lohmann [Optica Acta 6 (1959), 
319] provided us with the mathematical background, and we, at the I.T.C., made the 
verifying experiments. 
Measurements of dodging printers’ performance were carried out photographically, 
using a test plate that consisted of a square wave pattern, continuously decreasing in 
frequency (5% per step) of low contrast (0.3 D) and with mean densities of 0.3 D: 0.9 D: 
1.5 D and 2.1 D (figure 1). This test negative was then copied on dodging contact printers 
onto a soft gradation film. 
DENSITY DENSITY 
  
  
  
  
  
  
  
  
  
  
  
  
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FREQUENCY FREQUENCY 
| | Fig.1. Test negative. Schematic micro- Fig.2. Dodged copy on reversal film. 
densitometer recordings. Schematic microdensitometer recordings. 
Microdensitometer recordings of the copies show that — up to a certain frequency — 
the first fourier frequency is partly subtracted from the square wave pattern, depending 
on frequency and on mean density (figure 2). 
The dependency on the frequency is caused by the fact that the effective illumina- 
*) A detailed study will be published in the series “I.T.C.-publications”.