British Kinematography (1951)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

May, 1951 BOWEN, MOIR AND TURNER: TELEKINExMA SOUND EQUIPMENT 145 objects are out-of-focus when far ones are seen. In static stereoscopic pictures, the focus is usually sharp all over the picture so that time may be spent in looking from one object to another in the picture, the centre of interest changing. With a moving picture this is less needed, and the principal object only may be taken in sharp focus to accentuate the stereoscopic effect, while the rest is out of focus. Projection System In the projection system it is necessary therefore to provide an optical system cap [ able of giving definition sharp enough for the principal object to appear at any pari \ of the screen, leaving the out-of-focus effects : to the camera. Apparent depth in the picture is also assisted by a large angle of view so that no real objects outside the picture : come into view to spoil the illusion, for although many of the necessary factors are provided by the projection system it is still the psychological effect in the mind of the observer which fuses the images to produce one three-dimensional picture. This effect can be achieved by projecting each picture in the usual way, except that the two films must be in register on the screen, and must be held in synchronism. The use of two projectors requires that the lenses of the machines be separated by reason of the size of the machines, and to allow an operator to have access to both machines. This produces a parallax, different in direction for each machine, and the consequent keystone effects in the horizontal plane are in opposition. The righthand vertical edge of the left eye picture is therefore longer than that of the right eye picture and vice versa. This effect also takes place right through the picture, and spatial distortion would be introduced if it were not removed. It is true that this effect is present in the view of a correctly projected picture, but in this case it must be that due only to the inter-lens separation of the camera, which is decided upon by the producer and varies according to the desired dramatic effect. A rectilinear picture free from keystone effects from each machine is secured by off -set ting the lens of each machine, the right-hand lens to the left and the left-hand lens to the right. As mentioned previously, the right-eye picture is kept to the right eye by using a Polaroid filter between the projection lens and the screen, and by spectacles using Polaroid for each member ot the audience. The screen must be capable of reflecting polarised light while retaining the plane ot polarisation. The planes of polarisation are 90° apart and this gives transmission to one eye and a complete black-out for the other eye. Each picture is presented twice at 24 frames per second, with a black-out interval between each exposure. We may therefore present the right and left eye pictures alternately so that the screen is always illuminated and a better continuity of vision is maintained than is the case in flat pictures. The synchronous running of the two projectors is accomplished by the use of Selsyn motors which provide an electrical coupling between the two machines. The Selsyn motors are mechanically coupled at a oneto-one ratio to the normal driving motors. Using this arrangement, the electrical coupling has to take care only of the differences in speed of the two machines, and the torque transmitted from one machine to the other is very low. A chain and small diameter bonded fabric sprockets are used to couple the Selsyn and driving motors to keep down noise to a minimum. Framing Adjustments The framing adjustment normally used when the film is incorrectly threaded is now used to bring the two films into position to produce a right and left eye picture in register vertically on the screen. Horizontal register is achieved by lateral adjustment of the film in either gate, an Ardoloy pellet which steadies the guided edge of the film being provided with screw adjustment to effect this adjustment. In order to produce a rectilinear picture with the brightness curve centrally disposed about the screen centre, the projector mechanism unit was set at an angle to the lantern, so that the plane of the film in the