A method for testing system with a light source and an imaging device for the optic investigation of an object in remitted light and fluorescent light, the imaging device positioned with respect to a reference surface within a hollow space of a test apparatus, the reference surface having an indicator area with a wavelength-dependent optical property, where the optical property essentially varies between a first focal point of a first product of a first predetermined illumination spectrum and a first predetermined transmission spectrum and a second focal point of a second product of a second predetermined illumination spectrum and a second predetermined transmission spectrum. The method includes illuminating the reference surface with illuminating light from the light source and determining which illumination spectrum and which transmission spectrum are present in an observation beam path on recording the image.
