Patent ID: 7382455

Claim:
A filter wheel for a spectrophotometric optical system of a microplate reader, comprising a rotatable wheel body, at least one narrow-band filter with a relatively long central wavelength mounted to said wheel body, and at least one narrow-band filter with a relatively short central wavelength mounted to said wheel body, wherein said narrow-band filter with a relatively long central wavelength is provided with a diaphragm on a front surface thereof facing a lens of the system, said diaphragm being formed with a plurality of apertures, and wherein a ratio of a total effective area of said plurality of apertures to an effective area of said narrow-band filter with a relatively short central wavelength is equivalent to a ratio of energy amounts of shorter wavelength light passed through the narrow-band filter with a relatively short central wavelength to energy amounts of longer wavelength light passed through the narrow-band filter with a relatively long central wavelength when the diaphragm is not disposed.