The distance between two objects at which it first becomes impossible to resolve them as separate.
The
limit of
resolution is generally
represented with the
symbol "
D". In the context of microscopy and vision, the limit of resolution inherent to a particular device is defined as follows:
D = (.61 (lambda)) / (N sin a)
Where
lambda is the
wavelength of light used (smaller is better; limit of D for
visible light is about 200 nanometers),
N is the
refractive index of the material through which the light is passing (refractive index of air is one, more dense media have higher N and therefore better resolution (which is why many
microscopes use between the lense and
specimen)),
and
a is the angle or aperture, or 1/2 the angle of the cone of light produced.