The majority of cameras are purchased with a lens of ‘standard’ focal length for the film format. If the lens is not interchangeable, then it is almost certain either to be standard or slightly wide-angle for the format, or to have a short-range zoom lens including the standard value. The idea of the ‘ideal’, ‘normal’ or ‘standard’ focal length came from considerations of correct perspective in a photograph, viewing distance (D v) and the comfortable viewing cone of vision (see Chapters 22 and 23). A combination of large format (whole plate 6.5 × 8.5 inch), contact printing and lens FOV with good definition suggested that an EFL equal to the diagonal of the format would provide a useful arrangement; hence the standard lens.