Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix
| In electron-optical systems, (as well as light-optical systems), there are two major functions for lens: i) Lens work as an aperture because it can constraint the incident wave front. This is more easily understood for light-optical systems because the aperture effect is due to the finite surface area of the optical lens; ii) Lens can change the wave front, meaning after a wave front crossing a lens, the amplitude and phase factor of the wave will change.
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