def overlap_params(overlap, d_hkl, Lambda):
    """
    Calculate objective aperture, C_3 and defocus assuming Scherzer focus condition and three-beam CBED overlap.
    Params:
    d_hkl: d-spacing in Å.
    Lambda: wavelength in Å.
    Returns:
    objective aperture (mrad), C_3 (mm), defocus (Å).
    """
    theta_bragg = Lambda / (2 * d_hkl)
    theta_c = overlap * theta_bragg
    C_3 = (theta_c / 1.51) ** (-4) * Lambda
    defocus = -1.15 * C_3 ** (-1. / 4) * Lambda ** (-3. / 4)
    return theta_c * 1e3, C_3 * 1.e-6, defocus