Focus & astigmatism challenge

The controls below this image should allow you to try and correct for astigmatism (i.e. azimuthal focus-variation using the δf controls) as well as to optimize focus (over/under). Try optimizing the focus settings in this sense as best you can.

- - ⇓ electron phase-contrast image ⇓ - -

Parameters describing your final result can be revealed by hitting the "snapshot parameter values" button below. For a new random initial setting (or if the image above is blank), reload this page. Then see how close (on average) you in practice get to Scherzer-defocus (at -561±0 Å) with no more than say 60 clicks of those adjustment buttons after a page reload.


deFocus=±[Å] at angle=[deg]
Number of adjustment clicks=.

How much does the image that you prefer on average vary from the Scherzer-defocus value? It's possible for example that you prefer a sharper image i.e. one with higher spatial frequencies, which may e.g. be found at a considerably deeper underfocus value than the value with continuous contrast-transfer (and hence a first CTF zero) out as far as possible. To see what an image with corrected astigmatism might look like, hop over to our simulator test canvas here.

Thanks to the author of the javascript FFT routines we are using to do the calculations. This page is hosted by the University of Missouri Saint Louis Department of Physics and Astronomy. The person responsible for errors is P. Fraundorf, whose mobile-friendly electron detectives construction is here and whose most ancient webpage on electron phase-contrast focus optimization may be found on the web here.