Lichte focus

When a defocus amount is set at a value larger than Scherzer focus, a spatial frequency that leads the envelope function to 0 (zero) is increased. Then, the contrast transfer function starts to oscillate between positive and negative values at a lower spatial frequency than at Scherzer focus. In the case of reconstruction of an image by electron holography, the amplitudes with negative phase in the oscillation section can be added to the amplitudes with positive phase by converting the sign of the phase. In image reconstruction by holography, a structure image with a higher spatial resolution can be obtained by setting a defocus amount to a value twice or three times more than Scherzer focus. Such a defocus amount is named "Lichte focus" after the inventor of this technique.

Related Term(s)