In addition to retinal magnification, the reading field is an important concept for understanding the influence of the use of hand-held magnifiers on the reading process. Three possible horizontal reading fields can be distinguished: the monocular reading, field; the binocular reading field; and the composite reading field. In order to learn about the strategies that subjects use when reading with the aid of a magnifier, magnifier displacement was measured while subjects read texts under conditions that provided a variety of reading-field widths and text widths. It was found that individual subjects use different strategies (i.e. they use the monocular, binocular or composite reading-field width). In a following experiment for a large number of reading magnifiers the monocular field width was determined. In this experiment subjects were asked to define that part of the reading-field width which is free of aberrations. From these data the optimal width for reading magnifiers with different focal length can be specified.