This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Kodak Portrait Lens. The Kodak Portrait attachment is simply an extra lens that slips in front of the regular lens. It in no way affects the operation of the fixed focus kodaks, except that it makes a sharper picture at a distance of three and one-half feet, and, of course, throws more distant objects out of focus. (See Illustration No. 68.)
619. These Kodak Portrait attachments may also be used with any of the adjustable focus kodaks. After attaching the portrait lens to any focusing kodak, rack the bellows out until the pointer on the focusing scale points at fifteen feet. Place your subject at three and one-half feet from the camera and a good bust portrait can be made. Only bust portraits should be attempted with these attachments.
620. By changing the focus it is possible to place the subject at different distances from the camera, thus increasing or diminishing the size of the image. As the Kodak Portrait Lens is intended for use with film cameras which cannot be focused on a ground-glass, accompanying each portrait attachment is a printed table telling, in precise figures, the proper distance on the focusing scale required to correspond with the distance the subject is from the lens.
621. In all cases where portraits or pictures require a time exposure with the hand camera, the instrument must be attached to a tripod or rest on something solid, to prevent jarring of the camera during the exposure. For all portraits in the home at least three seconds' exposure should be given.