.CS [MM]: 2.0
[Enter the spherical aberration constant.]
.DEFOCUS(ANGSTROEMS), LAMBDA(ANGSTROEMS): 2000,0.037
[Enter the amount of defocus, in Angstroems. Positive
values correspond to underfocus (the preferred region);
negative values correspond to overfocus. Then,
enter the wavelength of the electrons. The value used in
this example corresponds to 100kV. Other values are listed
below:
keV A 100 0.03700 200 0.02501 300 0.01968 400 0.01643 ]
.NUMBER OF SP. FREQU. PTS.: 128
[Enter the dimension of the 2D array. In this example,
each element of the array (K,I) corresponds to a spatial
frequency
Kx = (K-65) * DK
Ky = (I-65) * DK
where DK is defined by the next input.]
.MAXIMUM SPATIAL FREQUENCY [A-1]: 0.15
[Enter the spatial frequency radius corresponding to the
maximum radius ( = 128/2 in our example) of pixels in the
array. From this value, the spatial frequency increment
(DK=0.15/64) is calculated.]
.SOURCE SIZE[A-1], DEFOCUS SPREAD[A]: 0.005,250
[Enter the size of the illumination source in reciprocal
Angstroems. This is the size of the source as it appears in
the back focal plane of the objective lens. A small value
results in high coherence; a large value, low coherence.
Next, enter the estimated magnitude of the defocus variations
corresponding to energy spread and lens current fluctuations.]
.ASTIGMATISM[A], AZIMUTH[DEG]: 400,30
[Enter the defocus difference due to axial astigmatism.
The value given indicates a defocus range of +/- 400A around
the nominal value as the azimuth is varied. Then, enter
the angle, in degrees, that characterizes the direction
of astigmatism. The angle defines the origin direction
in which the astigmatism has no effect.]
.Amplitude contrast ratio [0-1], Gaussian envelope halfwidth: 0.09,0.062
[Enter ACR and GEH (in A^1), see below for definition.]
.Sign (+1 or -1): -1
[Application of the transfer function results in contrast
reversal if underfocus (DZ positive) is used. To compensate for this
reversal and make the modified structure displayable by surface
representation, use the sign switch -1 above.]
The transfer function is now computed in complex 3D form, compatible with the Fourier transform format.
NOTES