CTF does not continue forever and the higher spatial frequencies are effectively damped out by envelope functions. The point where envelope functions damp the CTF to zero corresponds to the information limit of the microscope.
Effect of the envelope functions can be represented as:
where Ec is the temporal coherency envelope (caused by chromatic aberrations, focal and energy spread,instabilities in the high tension and objective lens current), and
Ea is spatial coherency envelope (caused by the finite incident beam convergence).
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CTF with only temporal coherency envelope applied
Philips Tecnai F20 ST
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CTF with only spatial coherency envelope applied
Philips Tecnai F20 ST
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CTF with both envelopes applied
Philips Tecnai F20 ST
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