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:
where a is the amplitude contribution (typically 0.07 for cryo and 0.2 for negative stain), and g(s) is the phase shift at reciprocal frequency s:
where Cs is the spherical abberation coefficient (typically around 2 mm), ∆f is the defocus (positive for underfocus), and l is the electron wavelength:
The defocus with astigmatism is:
