1. A method for calibrating an imaging system for imaging biological or chemical samples, the method comprising: for each of a plurality of initial effective distances from an optical component of the imaging system to a sample location, identifying an optimal focus setting of the optical component; and storing means for the imaging system to determine a first functional approximation that is derived from the optimal focus settings at the initial effective distances, the means being stored in at least one computer readable medium that is adapted to be communicably coupled with the imaging system, wherein the first functional approximation is operable for calculating an optimal focus setting for a new effective distance that is not one of the initial effective distances, the new effective distance being from a biological or chemical sample to the optical component.