Dimensional Measurement using Vision Systems - NPL Publications ...

Measurement Good Practice Guide No. 39
Figure 2: Airy disc intensity pattern.
Figure 3: Intensity sum of two airy patterns.
It will be seen later that other factors, including the coherence of the light, and the
numerical aperture of the condenser must also be considered in assessing resolution.
Nevertheless, expression (1) gives a reasonable guide to the resolution that can be
expected from a microscope objective working under normal conditions.
Equation (1) shows that the minimum resolvable object separation decreases with
increasing objective numerical aperture. Resolution figures derived from this expression
for typical microscope objectives are shown in Table 1 (assuming green light illumination
of wavelength 550 nm).
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