Optical EngineeringHighly accurate optical transfer function measurements: a new concept for the elimination of thermal expansion effects
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The optical transfer function (OTF) of calibration lenses must be measured with a high accuracy, requiring complex setups. Thermal expansion effects of the measuring system are a limiting influence, resulting in changes of the imaging state (e.g., defocusing) during the period of measurement. A new concept is presented to overcome these disturbing effects. By taking a rapid tomography sequence of image planes, the three-dimensional irradiance distribution in the image space is captured and stored in a computer, analogous to a flash photo of a moving object in conventional photography. After this, there is time to find the desired imaging state in the data. This "flash" concept has been successfully implemented in a typical OTF measuring setup, improving the reproducibility by one order of magnitude.