Examples using bctf
| A fan pattern with all spatial frequencies |
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| Part of a micrograph |
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Theory
The CTF's used in various software packages and given in many textbooks vary slightly but significantly. It is therefore important that the determination and application of CTF parameters be done with the same package. In Bsoft, the following version of the CTF is used:- CTF = amp_fac * cos(phase) - phi_fac * sin(phase)
The phase and amplitude contributions are related as:
- phi_fac = sqrt(1 - amp_fac*amp_fac)
The phase shift is given by:
- phase = 0.5 * PI * Cs * lambda^3 * s^4 - PI *
lambda *
defocus * s^2
The defocus with astigmatism is:
- defocus = defocus_average + defocus_deviation * cos(2 *
(angle -
astigmatism_angle))
- defocus_average = (defocus_max + defocus_min)/2
- defocus_deviation = (defocus_max - defocus_min)/2
The reciprocal space distance is:
- s = sqrt(x^2 + y^2)
The angle of astigmatism is:
- angle = y / x
The electron wavelength is:
- lambda = 12.26/ sqrt(volt * (1 + volt * 0.9788e-6)