Optical EngineeringVibration tolerance in optical imaging
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The effects of object-to-image vibration are studied with the purpose to quantitatively define the maximum acceptable vibration level as a function of resolution, linewidth control, exposure and focus toterances, proximity condition, and illumination coherence. The exposure-defocus trees and windows of optically projected images are used to derive the vibration tolerance as well as the optimum exposure as a function of vibration amplitude. Normalized variables for resolution, focus, and exposure are used so that the results are universally applicable for any given diffraction-limited lens system. Time histograms are used instead of the frequency spectrum to unambiguously define a given vibration environment. The results are plotted in depth of focus as a function of the vibration amplitude. Resolution ranges from 0.48 to 1.2 λ/NA with the aperture ratio σ = 0.4, 0.6, and 0.8. The optimum exposure for maximum depth of focus is similarly plotted.