THE KELL FACTOR
In practical scanning systems, the maximum vertical resolution realised is less than the actual number of lines available for scanning. This is because of the finite beam size and its alignment not coinciding with the elementary resolution lines.
Fig. 30.7 Effect of beam spot size on vertical resolution
Consider a finite size of a beam spot scanning a series of closely spaced horizontal black and white lines of minimum resolvable thickness, when the beam spot size is compatible with the thickness of the line, as shown in Fig. 30.7. If the beam is in perfect alignment the output will exactly follow the lines as black or ...