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Numerical aperture (NA)

The product of the refractive index of the medium between objective and specimen and the sine of the half-angle of the maximum light cone collected by the objective. Governs resolution, depth of field, and image brightness simultaneously.

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Related terms

Depth of fieldAbbe diffraction limitASTM E766Comparison microscopeEDX / EDXRFEmpty magnificationFluorescence microscopeInfinity-corrected opticsISO 8576Koehler illuminationParfocalityPlan objective

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