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.
42
BRITISH KINEMAIOGRAPHY
Vol. 21, No. 2
The mirror M, must reflect just the correct percentage of light to make each image the same brightness. This is about 39 per cent of the incident light, and therefore at full aperture (Fl .9) the effective aperture is about F3.0. (ii) Optical Registration
It is necessary to position the two images so that they are in exactly the correct relation with the sprocket holes on the film. This is achieved by using the camera as a projector in the following manner :
A film of a resolution chart is made by normal means, and a loop of this is threaded in the camera. Behind the camera gate is a prism, used for the " through the film " viewfinder. A normal condenser and lamp is used
able to make the film for setting up with the camera itself.
This can be done by achieving approximate alignment by the method above, and then photographing a transparent test chart held in the position formerly occupied by the cathode-ray tube screen. It is convenient to use the cathode-ray tube as the light source for this purpose. After development the film is loaded in the camera and the image projected on the face of the cathode-ray tube. If the film is loaded in the same position it occupied when being exposed then perfect superimposition will be obtained independently of the accuracy of optical alignment. If, however, it is displaced one frame, then alignment errors will be doubled. By making
Fig.
The optical system
and cross section
of shutter.
to illuminate the film through this prism, so that an image is formed on the cathode ray tube. If the mechanism is turned so that the shutter reveals both top and bottom apertures, a double image is formed, and it is relatively easy to adjust the mirrors so that superimposition is achieved.
It is important that the film used for achieving optical registration is of very high definition and free from kw bounce." The sprocket holes must also be undamaged, and the film should be of the same physical dimensions as the raw stock it is proposed to use. Since it is difficult to obtain 16 mm. films which meet these conditions it is desir
a loop of the film containing an odd number of frames it is possible to see both conditions one after another when the camera is running. The optical system is then adjusted to produce equal errors under both conditions. A further advantage of running the camera is that perforation tolerances then tend to be averaged. It has been found that if raw stock is exposed and hand processed immediately the shrinkage is negligible, although as the film dries out it may become intolerable.
The above alignment procedure enables substantially perfect alignment to be obtained, and the frame to frame position-errors are