An experimental study on the image quality loss of an objective caused by assemblage stress

Abstract

Stress birefringence caused by assemblage stress can change the light through the glass into tow beams in different polarization mode, so the magnitude of the stress birefringence can be measured by a polarimeter. The Modulation Transfer Function (MTF) curve can be looked as the accurate result of image quality of an objective, in this article, we make an analysis of the correlation in theory, and list the result of the experiment. The MTF curve shows the obvious difference before the stress caused by assemblage was released and after. The stress caused by assemblage produces the additive wave aberration of the light. This additive wave aberration then cause the image quality loss of the objective. Measurement data indicates another objective as contrast has no stress in any of its units, so the MTF curve was almost the same as it was designed. The most serious loss of the image quality by assemblage stress is the falloff of the vertical curve and the horizontal curve of MTF, especially at the edge of the view field of the objective, and once the stress of the lens was released, this falloff disappears at the same time. So our conclusion is before an objective was assembled, each lens must be test by a polarimeter. If the stress can't be accepted, the stress should be released forwardly. And, this kind of test should also be implemented before the stickiness of each lens of the objective for the final image quality.