If some annular portions of the lens are covered by opaque materials , the effective circular portion which pass the light will be less than the original diameter .
The latter is called aperture .
If there is no obstruction then the diameter of the lens will be the same as the diameter of the aperture .
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The latter is called aperture .
If there is no obstruction then the diameter of the lens will be the same as the diameter of the aperture .
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