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.
jects the point at R (red) and blue ray at B (blue). The green and yellow images will lie between the red and blue ones, and in place of a white image we will have a series of colored ones forming a spectrum. The length of this spectrum is a minimum when the stencil is located near the condenser and increases as the stencil moves towards the image of the source. The amount of this chromatic aberration depends only upon the power of the lens, its aperture and the magnification under which the source is imaged; in other words, if the location of the source and its image with reference to the lens and the angle a are given, the amount of chromatic aberration is determined. The thickness of the lenses has no influence upon it. Consider:
(b) The case of a perfect condenser and an extended light source. If the image of the light source is not point-shaped, the multitude of rays passing through a transparent point in the stencil causes a spot of light on the screen instead of a point, the size and shape of which is determined by the rays drawn from the object point through the differ
Projection of a transparent point P of a stencil T with an optically perfect condenser and an extended source. The projection of the point on the screen is not point shaped, but a patch of light ("circle of confusion"), the size and shape of which depends largely upon the size and shape of the source.
ent points of the image of the source. The figure 6 shows how the rays forming the image of the source and crossing at the object point pass from the light source through different parts of the lens. The size of the spot of light on the screen which represents the projection of an object point will depend upon the size of the source, or its image, as well as upon the location of the object point between the condenser lens and image of source. Projection in this simple manner is possible only if the detail of the object is coarse in comparison with the size of the image of the source. For projection of detail of a minuteness beyond a certain limit, a projection lens will have to be applied as will be shown later. Consider:
(c) The usual case of an imperfect condenser in combination with an extended light source. Instead of having one image of the source, each zone of the condenser will produce an image of the source at a different place of the optical axis and for each color contained in the radiation from the source a different series of such images will be produced. The projection of the point takes place as described above
49