This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

=================================================================================

Spatial resolution is defined as the smallest separation of two closely-placed structures which still permits them to be distinguished as separate.

For an optical microscope, the spatial resolution is given by,

          ----------------------------- [2711]

where,
         η -- The refractive index (e.g. = 1 for vacuum in EMs),
         sinα -- The numerical aperture,
         λ -- The wavelength of light.
For instance, for violet lights with 380 nm wavelength, d₀ is equal to 0.172 µm, while for electrons with 0.005 nm wavelength, d₀ is about 0.003 nm.