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

134 MOTION PICTURE PROJECTION This system has proven a great convenience to many of our customers and constitutes a real service which adds greatly to our detail in making and supplying lenses. Sometimes we are called upon to match or duplicate a lens we sold several months or years ago, and it is quite an advantage to the customer to get a new lens that will make the picture the same size it was before without any loss of time. It should be noted by every user of a projection lens that the components are not interchangeable and no liberty whatever should be taken with the arrangement or adjustment of a lens. A broken element cannot be replaced unless the complete lens is returned for repairs and the broken parts should be preserved as they may be useful in determining the exact original focal length, otherwise this may be changed by replacing the broken lens. Odd combinations or lenses are absolutely of no value and we cannot undertake to utilize them to make up complete lenses or for repairs. The condition of many lenses sent in to us indicates great carelessness in handling them and Projectionists should be cautioned to handle them more gently. There is positively no excuse for so many scratched surfaces, broken lenses and ruined mounts after allowing for reasonable accidents. The terms quarter and half size have no real place in optical nomenclature although commonly used. No doubt they originated in the early days of photography when applied to portrait lenses used for quarter size (3/4x4%) and half size (4)4x6^) cameras. These were the first lenses used for projection and eventually each size was made in a number of different