Method: each detector/ camera images a diffraction limited fluorescent source. This can be performed using the internal light sources and a fluorescent bead sample or an etched fluorescent pattern covering the field of view. A minimum standard would be recording the field of view for each high resolution objective over the widest field of view for the commonly used fluorescent channels over an axial range close to the cover slip. Ideally, all excitation options would be covered, and deeper PSFs would also be measured.
Justification: this allows monitoring of objective quality and other system parameters (eg immersion oil). Comparison of PSFs over time for each objective will identify any new aberrations in the system (eg damaged/ unclean objective, defective oil). The data can be obtained from the same data set as the chromatic aberration if multi wavelength emission diffraction limited spots/ beads are used for that test. The data can be used for post acquisition correction if required (eg deconvolution), and can be reported with published data to prove the resolution limitations of the system.