Environmental Factors Degrade Optical Performance
When optical systems become exposed to a non-ideal environment, their optical performance degrades. For example, a lens system which was designed to produce high quality images may produce poor quality images when subjected to the thermal effects of a laser beam. Some of the energy in the beam is absorbed by each lens, causing temperature gradients throughout each lens that deform the lens surfaces. A second effect of the temperature gradients is a change in the indices of refraction, optical material properties that are dependent on temperature. A third and less important effect is that the temperature gradients induce stresses that also change the indices of refraction. These combined effects cause image quality to decline.
As any camera buff knows, another common environmental factor affecting optical performance is vibrations. Any optical imaging system which produces quality images in a stable condition will produce lower quality images when subjected to vibrations coming through its support condition. In the case of a handheld camera the source of vibration is the instability of the person holding it. In the case of a high performance imaging system possible sources of vibration are cooling equipment, altitude control gryroscopes, aircraft vibration, and other ambient vibration sources.
A good design team must be able to predict the effects of the environment on their optical system in order to optimize their design to mitigate such effects. Such performance prediction requires the proper tools. In the examples above, MD Nastran can predict the mechanical behavior quite well. To predict optical performance, SigFit is required to convert the results from MD Nastran into a form suitable for optical analysis software.
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