Motion picture projection; an elementary text-book (1921)

130 MOTION PICTURE PROJECTION It is our opinion that the quality of the picture is more important than its size, or, in other words, we must have perfect projection as the first consideration. Owing to the unavoidable loss in definition and illumination incidental to an increase in magnification it is advisable to keep the size of the picture within a reasonable limit which we think is about 12x16. Above this size the surface area increases very rapidly with each additional foot in width. The distance the picture is projected is not so important unless it necessiates the use of lenses of abnormally short or long focus. Theoretically, there is a loss of light in inverse ratio to the square of the distance, but in practice a picture of a given size can be projected within a reasonable distance without any noticable change in luminosity. Obviously this imposes a limitation to the size of theatres, therefore it is not advisable to make a theatre so large that good projection cannot be secured. The best results are obtained with lenses ranging between 4" and 7^" focal length and any deviation from these is not advisable. The picture is projected from the same film whether it is thrown 25 ft. or 150 ft. while an enlargement of the picture is secured only by magnification of the film image with a consequent depreciation of the light by spreading it over a greater surface. The definition is impaired as the natural result of magnifying a film image which is not absolutely sharp to begin with. On the contrary, a difference in the distance does not bring these factors into consideration although other difficulties arise if an effort is made to produce too large a picture with