Stray Light In Optical System Research Articles

Crosstalk in monocentric multiscale systems based on an internal stray light stop suppression method.

Monocentric multi-scale (MMS) systems offer the advantages of a high resolution and wide field of view (FOV). These systems can improve the image resolution with a broad FOV by utilizing the stitching of the detectors. In addition to traditional stray light in optical systems, such as ghost reflection, scattering, and diffraction, the crosstalk between relay lenses cannot be ignored as a type of special stray light. Because of the intersection rays between the multiscale relay lenses in MMS systems, the rays enter the adjacent relay lens, which generates rays that do not belong to the corresponding relay lens in the corresponding image plane. Consequently, this crosstalk stray light affects the imaging contrast of the systems. This study aimed to investigate the crosstalk stray light in MMS systems. A simulation model of the MMS system was established. In the object-imaging process, the characteristic rays of a multiscale relay lens are traced using geometrical optics. Factors affecting the crosstalk stray light were studied in detail. The relationships between different parameters and crosstalk stray light were analyzed. A stray light suppression method is proposed based on incorporating a stray light stop in a monocentric (MC) objective to cut the crosstalk stray rays. The simulation results show that the crosstalk stray light can be effectively eliminated with this method, and the image contrast of the MMS systems is greatly improved.

On the Flare of Lenses

The flare or the stray light in optical systems reduces the image contrast in photography and causes serious errors in photometry. The amount of the flare for small luminous objects was measured by an improved photographic photometry. Generally, the flare originates in two ways, that is, reflections at air-glass interfaces and scatterings by dusts or scratches on glass surfaces. The flare by reflection increases with the area of the illuminated object and attains a saturated value for a large field angle: on the other hand, the flare by scattering slightly depends upon the area. When plotted versus the area or the square of the subtended angle of the target, the amounts of the flare lie on a straight line with several kink points, and the flare by scattering can be determined by extrapolating this line to zero field angle. For a small luminous target, the effect of the flare by reflection is less at a higher relative aperture than at a lower, and the anti-reflection coating greatly reduces the reflected light but slightly enhances the scattered light.

Stray Light in Optical Systems*

An objective method has been developed for measuring the stray light in optical systems. Stray light reduces the contrast of image and falsely appears to augment the light transmission of optical system. The method utilizes a photoelectric apparatus to compare the contrast of an image formed by an optical system with the contrast of the object under examination. This comparison, when expressed on a percentage basis, is referred to as “the contrast rendition” of the optical system. The contrast rendition of telescopic, photographic, and microscopic systems has been studied under a variety of conditions. It has been found that the contrast rendition values range from 3 to 100 percent for the systems studied. The contrast rendition of an optical system has been found to depend upon its optical and mechanical design, the use of reflection reducing films, surface defects, the cleanliness of its optical surfaces, the use of lens shades, and the brightness condition of the region surrounding the object under examination. The contrast rendition, for large targets and for a uniform surround, has been found to be independent of the brightness level at which the measurements are made, the contrast of the object, the field angle, and the optical aberrations present in the systems examined. The importance of contrast rendition in telescopic systems has been evaluated using the methods and data of Hardy, Duntley, and Blackwell. This evaluation was made by comparing the computed loss in range that would be caused by an imperfection in contrast rendition with the loss caused by an equal imperfection in light transmission and in magnification for telescopic systems. It was found, for all brightness levels, that the contrast rendition was generally more important than the other two variables. Because of the indicated strong dependence of the range at which targets are visible upon contrast rendition, ranges were computed for specific objects, instruments, and observation conditions, and compared with the results of an extensive visibility field test conducted from aboard ship. The computed and observed ranges were found to be in close agreement. This indicates that the contrast rendition of an optical system is a major factor in determining its performance.