In complex biological samples, the concentration of off-target molecules is usually significantly higher than the target molecules. Therefore, even in the absence of recognition elements the off-target molecules readily adsorb to the surface of the sensor. However, this a random process and the off-target molecules do not bind to the ordered binding sites of the mologram. Thus, scattering of off-target molecules is uniform in all spatial directions and therefore off-target molecules hardly contribute to the measured light intensity in the narrow solid angle of the focal spot. In essence, focal molography forms a high-frequency spatial affinity lock-in that only measures the Fourier component of the refractive index distribution that corresponds to the binding modulation of the mologram. Since the environmental noise (temperature gradients, buffer changes and nonspecific binding of off-target molecules) is inversely proportional to the spatial frequency and therefore situated mostly at "long" spatial periods most of the noise can be rejected. This property makes molography extremely robust and renders temperature stabilization or sensor equilibration obsolete.