Top: examples of LR K-band AMBER interferograms of NGC 3783 (~2.0–2.4 μm from bottom to top), which illustrate the noise problem. From left to right, the first and second interferogram are recorded with UT2–UT3 (46.6 m projected baseline) with DIT = 800 ms and 400 ms, respectively, the third one with UT3–UT4 (62.5 m, 800 ms), and the last one with UT2–UT4 (89.4 m, 800 ms). Middle: calibrated visibilities of NGC 3783 and geometric ring-model fit (red). We derive a ring-fit torus radius of 0.74 ± 0.23 mas or 0.16 ± 0.05 pc. Bottom: closure phases plotted versus wavelength.