Systems and methods for assessing biological samples

An instrument for biological analysis, comprising:

• an excitation source;
• an optical sensor configured to receive emissions from one or more biological samples in response to the excitation source;
• an excitation optical system disposed along an
• excitation optical path;
• an emission optical system disposed along an emission optical path;
• a sensor lens configured to direct emissions from at least some of the biological sample onto the optical sensor;
• a heated cover disposed in the excitation path configured to prevent condensation above the biological samples contained in a sample holder, the heated cover having an illuminated surface disposed along the excitation optical path, the illuminated surface configured to produce reflected radiation comprising radiation from the excitation source that is reflected by the illuminated surface;
• and
• a radiation shield,
• wherein:
• the radiation shield comprises a sensor aperture disposed along the emission optical path and a blocking structure configured to cooperate with the sensor aperture such that, of the radiation which is reflected by the illuminated surface, only that is subsequently reflected by another surface of the instrument is received by the optical sensor.