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| Transmitted light – bright field |
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In practical microscopy, you do not always have nicely stained samples which are easy to view in simple brightfield. Unstained samples, such as bacteria or living cell cultures, absorb practically no light and are barely or not at all visible in brightfield, even in a well-aligned microscope. The poor light absorption results in extremely small differences in the intensity distribution in the image. With a bright background, the human eye requires local intensity fluctuations of at least 10 to 20% to be able to recognize objects.
This “modulation” of light intensity is far from reached by many microscope objects in brightfield. The contrasting techniques described in the following are tricks which allow optical effects in the sample – not visible to the eye – to be translated into intensity changes which can be recognized by the eye.
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