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Practical Digital Photomicrography: Photography Through the Microscope for the Life Sciences by Brian Matsumoto

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9.6. Extending the Depth of Field

Optical systems have only one plane of focus that is absolutely sharp; regions above and below that plane show a progressive loss of sharpness. In general photography, the drop-off in sharpness is gradual, and for a given lens and distance, a relatively wide zone appears to be sharp. This zone can be controlled by closing down the lens diaphragm and increasing the depth of focus—an advantage in landscape photography for showing vast expanses with fine detail.

However, a narrow depth of focus may be desirable for certain compositions. In portraiture work, the photographer seeks to have the face in focus and renders the background areas blurred by throwing them out of focus. This serves to concentrate the viewer's ...

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