The invention relates to a device for detecting a sample in a longitudinal sample container (10), comprising a sample container holder (30) for holding the sample container in a housing. Said sample container holder comprises a side viewing window in the region of at least one longitudinal side of the sample container, and a front viewing window (35) in the region at least one front side of the sample container. Said device also comprises a first illumination arrangement for illuminating the sample container through the front viewing window, a second illumination arrangement for illuminating the sample container through the side viewing window, and an imaging photodetector for detecting a first image of the sample illuminated by means of the first illumination arrangement, and a second image of the sample illuminated by means of the second illumination arrangement. Said detection takes place through the side viewing window. Said device further comprises a digital data processing unit for overlaying the first and second images and for representing the resulting overlay image on a display device connected to the data processing unit.