CTF > 0 (positive contrast)
CTF < 0 (negative contrast)
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Every image collected in a cryo-electron microscope is stamped with the instrument's contrast transfer function (CTF) — an oscillating filter set by defocus, spherical aberration and accelerating voltage that flips the sign of contrast at a series of spatial frequencies, producing the concentric "Thon rings" visible in a micrograph's power spectrum. This simulator renders the 2D CTF as a live 3D surface: each bar's height and color encode CTF(k) at that spatial frequency, so the rings you see are literally the zero crossings where signal disappears or inverts. Adjust defocus, spherical aberration, accelerating voltage and the B-factor envelope to see how each parameter reshapes the rings, while live readouts track the electron wavelength and the resolution of the first zero crossing — the exact quantities a real CTF-estimation step (CTFFIND, Gctf, patch-based fitting) recovers before phase-flipping or Wiener-filtering the data ahead of 3D reconstruction.