Patent ID: 7595881

Claim:
An optical system for measuring fluorescence from a liquid contained in a vessel, comprising: a) a light source and a first lens for collimating excitation light from said light source into a beam of excitation light, a reflective mirror positioned to receive and redirect the beam of excitation light in a first direction along an axis of a vessel located in a vessel holder located on one side of said reflective mirror, a second lens positioned along said axis on said one side of said vessel between said reflective mirror and said vessel for focusing said beam of excitation light onto said vessel and collimating light emitted from the liquid in said vessel; b) a third lens symmetrically disposed with respect to said axis of said vessel and located on a second side of said reflective mirror, for focusing light collimated by said second lens onto a first detection means; and c) said second lens having a diameter larger than a cross sectional area of said reflective mirror transverse to said axis such that some excitation light scattered from refractive surfaces within the vessel including a liquid meniscus is rejected by said reflective mirror, but some fluorescent light emitted by the liquid in said vessel bypasses the reflective mirror and is focused onto the detection means by said third lens; wherein said optical system includes a shadow disc symmetrically disposed with respect to said axis located between the said reflecting mirror and said third lens, wherein a diameter of said shadow disc is greater than that of said cross sectional area of said reflective mirror transverse to said axis but less than the diameter of said second lens such that excitation light scattered from refractive surfaces within the vessel including a liquid meniscus is rejected by said shadow disc, but some fluorescent light emitted by the liquid in said vessel bypasses the reflective mirror and is focused onto the detection means by said third lens.