CTF Estimation¶

Image formation in EM is distorted by modulation of a contrast transfer function (CTF). Distortion depends on the physical parameters of the microscope, such as keV and lens abberations. Correcting for these aberrations is done by comparing the experimentally observed power spectral density (PSD) of EM images to a theoretically generated CTF.

Available CTF Procedures:¶

1. Ace Estimation
2. Ace 2 Estimation
3. CtfFind Estimation
4. gCTF Estimation

Appion SideBar Snapshot:¶

Notes, Comments, and Suggestions:¶

Appion CTF parameter definition

If you have a large range of defocus in your data, one parameter set or even one estimation method may not work for all of them. In this case, you can start a separate run but choose a different parameters that only process those with low confidence results. Next appion processing (stack making) will pick the result with highest confidence value image by image to be used. Note that Ace and Ace 2 have in general equivalent confidence values while CtfFind values tend to lower which makes it harder to mix and match currently. See forum http://emg.nysbc.org/boards/13/topics/990

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