A microtiter plate reader apparatus for measuring an optical component (160, 170, 190) of the apparatus, the apparatus comprising: a light source configured to form a measuring beam in a measuring channel, the measured optical component being configured to be in a first position outside the measuring channel and in a second position in the measuring channel; a first detector, located in the measuring channel, configured to receive beams in the measuring channel; wherein the measuring channel is integrated to a photometer channel or a fluorescence channel of the apparatus, wherein the photometer channel or the fluorescence channel is configured to be used when measuring a sample using the apparatus, and the apparatus further comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus at least to: measure a first beam, using the first detector, in the measuring channel, wherein the measured optical component is in the first position; measure a second beam, using the first detector, in the measuring channel, wherein the measured optical component is in the second position between the light source and the first detector; and determine optical characteristics of the optical component based on the first beam and the second beam. a light source configured to form a measuring beam in a measuring channel, the measured optical component being configured to be in a first position outside the measuring channel and in a second position in the measuring channel; a first detector, located in the measuring channel, configured to receive beams in the measuring channel; wherein the measuring channel is integrated to a photometer channel or a fluorescence channel of the apparatus, wherein the photometer channel or the fluorescence channel is configured to be used when measuring a sample using the apparatus, and the apparatus further comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus at least to: measure a first beam, using the first detector, in the measuring channel, wherein the measured optical component is in the first position; measure a second beam, using the first detector, in the measuring channel, wherein the measured optical component is in the second position between the light source and the first detector; and determine optical characteristics of the optical component based on the first beam and the second beam. at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus at least to: measure a first beam, using the first detector, in the measuring channel, wherein the measured optical component is in the first position; measure a second beam, using the first detector, in the measuring channel, wherein the measured optical component is in the second position between the light source and the first detector; and determine optical characteristics of the optical component based on the first beam and the second beam. measure a first beam, using the first detector, in the measuring channel, wherein the measured optical component is in the first position; measure a second beam, using the first detector, in the measuring channel, wherein the measured optical component is in the second position between the light source and the first detector; and determine optical characteristics of the optical component based on the first beam and the second beam.