Commercial Projectors

The persistence of vision should be compared with the related phenomenon of Beta Movement and the Phi Phenomenon. A critical part of the understanding of the aspect of visual perception is that the eye is not a camera; that is, there are no "images per second" in the eye. Instead, the eye/brain system has a combination of motion detectors, detail detectors, and pattern detectors, the results of which combine to create the visual experience.

The frequency at which the change of images becomes invisible depends on the level of illumination. Generally, 16 images per second (or, of English, frames per second: fps) is considered the lowest frequency at which humans perceive continuous movement. (It is interesting to note that this threshold varies between different species, a higher proportion of rods in the retina result in a higher threshold frequency).

It is possible to appreciate the space between images by closing and opening the eyes quickly. If it's done fast enough, at some point the transition will be caught. This will not work with television due to the persistence of phosphorus or with LCD or DLP projectors due to the continuity of the image, although some digital projection technologies can show artifacts.

Since the birth of sound cinema, almost all commercial cinema projectors project at a frequency of 24 images per second. This speed was chosen for financial and technical reasons: it was the lowest frequency (so it required less film) to which satisfactory reproduction and amplification of sound could be made. There are, however, some special formats such as Showscan or Maxivision that project at higher frequencies, often 48 images per second.

Silent films were not usually projected at constant speeds, but varied during projection at the discretion of the projectionist, often by notes provided by the distributor. In Spain, one of the leading manufacturers of film projectors was the company Ossa de Barcelona, ​​also known as a motorcycle brand.