Contrast transfer function
The contrast transfer function is the equivalent of the optical transfer function in light that affects images collected in a transmission electron microscope. The contrast transfer function must be corrected in the images in order to obtain high resolution structures in three-dimensional electron microscopy, especially cryo-electron microscopy.
where . The function is defined as:
where r is the radius from the center of the image, Cs is the spherical aberration, λ is the wavelength of the electron beam (usually converted from the potential difference voltage) and z is the amount of defocus (using the convention that underfocus is negative and overfocus is positive)
where is the average defocus and is the difference between the maximal and minimal defocus in the CTF. Where the defocal difference is defined such that:
- Optical transfer function
- Point spread function
- Contrast transfer function (CTF) correction
- Airy disk, different but similar phenomena in light
- Talk on the CTF by Henning Stahlberg
- CTF reading list
- Spence, John C. H. (1988 2nd ed) Experimental high-resolution electron microscopy (Oxford U. Press, NY) ISBN 0195054059.
- Ludwig Reimer (1997 4th ed) Transmission electron microscopy: Physics of image formation and microanalysis (Springer, Berlin) preview.
- Earl J. Kirkland (1998) Advanced computing in electron microscopy (Plenum Press, NY).
- Malick, S.P. (2005). "ACE: Automated CTF Estimation". Ultramicroscopy 104 (1): 8–29. doi:10.1016/j.ultramic.2005.02.004.
- Maxim V. Sidorov. "What Is CTF (Contrast Transfer Function)?". ctfExplorer. Retrieved July 29, 2011.
- Mindell, J. A.; Grigorieff, N. (2003). "Accurate determination of local defocus and specimen tilt in electron microscopy". Journal of structural biology 142 (3): 334–347. PMID 12781660.