Working with IBR/BTF data requires a complete calibration. Modern setups speed up recordings by using multiple lamps and cameras. Therefore, the calibration task gets more time consuming and challenging, especially for an accurate calibration of multiple light sources. Most works are dedicated to the calibration of cameras, whereas the light field calibration problem remains as a rule overlooked. Our experiments have shown that the spatial variance of light strength can be vigorous, inducing serious damage to the IBR/BTF data. We propose a novel method based on Helmholtz reciprocity, which derives light field information directly from the target IBR/BTF data rather than from specially dedicated calibration objects. Instead of repeating the recording of a huge number of images, only one additional image is needed.