A camera is provided for detecting three-dimensional image data from a detection zone that has an illumination unit for transmitting transmitted light that is modulated at a first modulation frequency, an image sensor having a plurality of reception elements for generating a respective received signal, a plurality of demodulation units for demodulating the received signals at the first modulation frequency to acquire sampling values, a reference illumination unit for transmitting reference light that is modulated at the first modulation frequency and is guided to the image sensor within the camera, and a control and evaluation unit. In this respect, the control and evaluation unit is configured to distribute reference part measurements for a functional test over a plurality of distance measurements.