Dirkjan: Created page with "In Scherzer defocus, one aims to choose the right defocus value Δf one flattens χ(u) and creates a wide band where low spatial frequencies u are transferred into image inten..."

2020-08-25T09:01:47Z

Created page with "In Scherzer defocus, one aims to choose the right defocus value Δf one flattens χ(u) and creates a wide band where low spatial frequencies u are transferred into image inten..."

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In Scherzer defocus, one aims to choose the right defocus value Δf one flattens χ(u) and creates a wide band where low spatial frequencies u are transferred into image intensity with a similar phase. In 1949, Scherzer found that the optimum defocus depends on microscope properties like the spherical aberration Cs and the accelerating voltage (through λ) in the following way:

[img[http://tiddly.vanwill.com/uploads/workspace/default/ScherzerFormula.JPG][EmbeddedImages]]

where the factor 1.2 defines the extended Scherzer defocus. For example, when Cs=0.6 and an accelerating voltage is 300keV result in ΔfScherzer = -41,25 nm.
The [[point resolution|point resolution]] of a microscope is defined as the spatial frequency ures where the CTF crosses the X-axis for the first time. At Scherzer defocus this value is maximized.

[img[http://tiddly.vanwill.com/uploads/workspace/default/Scherzer.JPG][EmbeddedImages]]
[[Category:microscopy]]

Scherzer defocus - Revision history

Dirkjan: Created page with "In Scherzer defocus, one aims to choose the right defocus value Δf one flattens χ(u) and creates a wide band where low spatial frequencies u are transferred into image inten..."