The directed bright-field (see Fig. 1) has extremely strong directional characteristics by means of a point source and an optical system (condenser); in this case, each point of the photographic film receives light from only one direction.
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On the other hand, in a diffused bright-field setup (see Fig. 2) the illumination of the film is provided through a translucent slab (diffuser), and each point of the film receives light from all the directions.
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In the absence of scattering, the attenuance provided by the emulsion is independent of the collimation of the illumination; a dense point absorbs a big portion of light and a less dense point absorbs a smaller portion, irrespective of the directional characteristics of the incident light.
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