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.
166 HANDBOOK OF PROJECTION FOR
from which the polish of the lens has been burned by impact with incandescent bits of carbon or metal. The light rays striking the lens at this spot are diffused, and a greater percentage of the light is reflected from such a spot than would be reflected if the polish were perfect. All the light not reflected by the unpolished spot of course passes through the lens, but reaches its other surface in the form of more or less perfectly diffused light and it is problematical just what percentage of it the three remaining lens surfaces which it must pass through will redirect and converge to the spot.
In the absence of any known tests to determine the loss occasioned thus we can only say that it is fair to assume it to be considerable; also it seems to us that a pitted condenser must necessarily place a considerable additional strain on the optical properties of the rest of the system, which may result in loss of definition of the picture. Of this we are not entirely certain, but believe it to be true.
In any event, bearing in mind the fact that condenser lenses are a comparatively cheap commodity, and that any injury to the screen result will inevitably result in the sale of less seats, we would suggest that it is poor policy to use a badly pitted condenser lens. Better throw it away and install a lens that you know is all right.
THICKNESS OF LENSES.— Projectionists will have observed that some condenser lenses have a very thick edge, and some a rather thin edge. The condenser lens should by all means be standardized in these dimensions. It is necessary that a condenser lens edge have at least l/16th of an inch thickness, because if it were brought right down to a sharp edge the tendency to breakage would be greatly increased. l/16th of an inch is, however, ample, insofar as prevention of breakage be concerned, and since additional thickness of a glass tends in any event to absorb light energy to some extent, especially if the glass be of poor quality, it therefore follows that condenser lenses should have a standard edge thickness of l/16th of an inch, thus minimizing the thickness of the lens.
In Fig. 37 we see at A a lens having unnecessary edge thickness, and at B a lens having the correct thickness of edge. Condenser lenses should have standard 4^2 inch diameter — not pretty nearly but exactly. Another point is that the more nearly lens edge thickness and diameter be exactly standardized the more nearly will projector manufacturers be able to make condenser mounts which will properly receive and support the lens.