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Early microscopists relied on oil lamps and natural sunlight to provide an external source of illumination for their primitive (but often remarkably accurate) microscopes. They often employed rather ingenious methods of gathering light, such as reflection from a large white board or scattering of sunlight on a cloudy day. Unfortunately, these methods did not provide reliable illumination and frequently the area of field illumination greatly exceeded the numerical aperture of the objective, causing glare and flooding.
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