A THEORY OF SCANNING 501 



This figure for the degradation must be taken with a certain reserve, 

 partly because the exact telegraph theory for the criterion of resolution 

 considered has really been inferred rather than presented in complete 

 logical form, and partly because the figure may be expected to vary 

 according to the criterion of resolution chosen. Some rough studies 

 have indicated the degradation to be materially less if the more con- 

 ventional criterion of resolution (two parallel line sources of light) were 

 used. 



This degradation may be estimated in another manner. In Ap- 

 pendix II the extraneous components have been computed for a variety 

 of apertures and degrees of overlap between adjacent scanning lines. 

 In Fig. 19 there have been plotted the maximum amplitudes of these 



APERTURES 



f<^ 



o 



o 



! 1.5 2.0 2.5 3.0 3.5 4.0 



BLURRING RELATIVE TO SQUARE APERTURE OF SCANNING PITCH WIDTH 



Fig. 19 — Magnitude of extraneous components as a function of resolution. 



extraneous components in each case (the first and second extraneous 

 patterns being plotted separately) as a function of the relative coarse- 

 ness of resolution for the normal image alone. This latter quantity is 

 taken relative to a rectangular aperture of width equal to the scanning 

 pitch, and, for example, for a rectangular aperture of width equal to 

 twice the scanning pitch, is represented by the figure 2. For conveni- 

 ence, above the various points have been inserted small diagrammatic 

 representations of the corresponding apertures. Also for convenience 

 the points have been arbitrarily connected together. 



From inspection of Fig. 19 several conclusions may be drawn, 

 namely, 



