A system for imaging microscopic samples, comprising: a light source (31, 210) for exciting fluorescence from at least one sample; a microscopic setup comprising an optical excitation path comprising one or more objective lenses which direct light from the light source to an object plane coincident with the at least one sample, and a microscope tube lens; a reference beam splitter disposed in the optical excitation path and configured to separate a part of the light from the optical excitation path; a photosensor (22, 40, 230) configured to detect the part of the light separated from the optical excitation path and output an electrical signal representative of optical flux to the at least one sample; a camera (30, 280) disposed on the microscope setup and configured to capture an image of fluorescence light emitted from the at least one sample; and a controller comprising an integrator configured to integrate the electrical signal from the photosensor and produce an integrated output and a comparator configured to compare the integrated output to a predetermined threshold, wherein the controller at least is adapted to control an exposure time of the camera (30, 280) such that each sample receives substantially the same total optical flux during a duration of camera exposure which is terminated when the predetermined threshold is reached, characterized by a beam splitter configured to direct light emitted by the light source along the optical excitation path to the reference beam splitter where a part of the light passes to the photosensor (22, 40, 230) and another part of the light passes to the at least one sample, wherein the light emitted from the at least one sample travels backward through the optical excitation path passing through the reference beam splitter, the beam splitter and the microscope tube lens before arriving at an image plane of the camera (30, 280). a light source (31, 210) for exciting fluorescence from at least one sample; a microscopic setup comprising an optical excitation path comprising one or more objective lenses which direct light from the light source to an object plane coincident with the at least one sample, and a microscope tube lens; a reference beam splitter disposed in the optical excitation path and configured to separate a part of the light from the optical excitation path; a photosensor (22, 40, 230) configured to detect the part of the light separated from the optical excitation path and output an electrical signal representative of optical flux to the at least one sample; a camera (30, 280) disposed on the microscope setup and configured to capture an image of fluorescence light emitted from the at least one sample; and a controller comprising an integrator configured to integrate the electrical signal from the photosensor and produce an integrated output and a comparator configured to compare the integrated output to a predetermined threshold, wherein the controller at least is adapted to control an exposure time of the camera (30, 280) such that each sample receives substantially the same total optical flux during a duration of camera exposure which is terminated when the predetermined threshold is reached, characterized by a beam splitter configured to direct light emitted by the light source along the optical excitation path to the reference beam splitter where a part of the light passes to the photosensor (22, 40, 230) and another part of the light passes to the at least one sample, wherein the light emitted from the at least one sample travels backward through the optical excitation path passing through the reference beam splitter, the beam splitter and the microscope tube lens before arriving at an image plane of the camera (30, 280).