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.
356 PRINCIPLES OF CINEMATOGRAPHY
train, the gears are slightly displaced in a direction along their shafts so that gear 'E' is caused to be so far out of line from gear 'A' that it will not engage with this gear at all it is, in fact, so positioned that it can only engage with gear 'B'. Gears 'D' and 'E' are mounted on bearings housed in the link system 'F', 'G' and 'H\ These links, together with line 'L-M' (which passes through the centre of gears 'A' and 'C) form a parallelogram, the angles of which may be adjusted by setting control lever 'P\ The mechanism is shown again in 'position T after lever 'P' has been raised to its uppermost position.
The operation of this mechanism can be more easily understood by assuming for the moment that gear 'A' is stationary. Since gear 'C is mounted in a fixed centre and is in mesh with gear 'A', it follows that this gear must also remain stationary. If, under these conditions, lever 'P' is then moved from 'position 1" to 'position 2', gear 'D' will be forced to rotate about gear 'C\ Such rotation will then be transmitted to gear 'E' and, through this gear to gear 'B\ Thus, by moving lever 'P', gear 'B' may be caused to rotate with respect to gear 'A'. Obviously, such an operation can be carried out with equal success when the camera is running and gear 'A' is rotating at a constant speed.
Lens Turrets
A further refinement, which is supplied with many cameras, is a mounting whereby a selection of lenses may be located at will in front of the film aperture. Most cameras which include this feature have a large circular turret upon which three or more lenses may be mounted and which also forms a housing in which the shutter may rotate. Lenses are available which will cover different fields when the camera is mounted in one position. For example, if a camera is mounted so that the normal field of view when using a 1-inch (25-mm) lens is of the order shown at 'A', Figure 154 -that is, a so called 'medium close shot' it will be possible to rotate the lens turret to bring either a telephoto or a wide-angle lens into operation and so produce either the 'big close up' shown at 'B' or the 'medium long shot' shown at 'C without moving the camera or altering the set-up in any way.
It should of course be realised that the 'depth of field' of a lens varies according to its 'focal length' and also the 'aperture' at which it is working. When any lens is critically focused to a given distance it will be found that objects placed either slightly infront or slightly beyond this critical distance will also be focused with quite tolerable sharpness. The range of distances over which