Patent ID: 7205518

Claim:
An arrangement for mitigating the effect of surface reflection in measuring the position of a focus in an optical measuring apparatus, wherein a measured object comprises a sample present in a sample vessel and for measuring the position of a focus, the measuring apparatus comprises: a light source for applying a light beam to an object to be measured; and a detector ( 770 ) for measuring light reflected from the measured object; whereby at least a portion of the light beam to be measured has reflected from a junction between the sample and a wall of said sample vessel, as well as a portion has possibly reflected from a junction between the wall and air, characterized in that said arrangement comprises at least one polarization filter for filtering said light beam, and said sample vessel wall consists of a material, in which the polarization state of a light beam changes as the light beam advances through said wall, the polarization filter ( 721 , 751 ) having its polarization direction selected in view of applying more suppression to the portion of a measured light beam reflected from the wall/air junction than to the portion reflected from the sample/wall junction.