The FWHM is the same for all point-sources in the image (if opticalaberrations can be neglected).
如果光学系统引起的像差可以忽略,那么影响各星点的FWHM都将是一样的。
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Enthusiasts still clamor for the film cam, whose poor construction yields mysterious opticalaberrations and sometimes doesn't even bother to keep images from seeping across the film's sprocket holes.
The optical engineer must make tradeoffs in controlling aberrations to achieve the desired result of the design. Here are some aberrations found in different types of telescopes