The brief chapters of his work have been justly compared to the laisses or tirades of a chanson in what may be called the vignetting of the subject of each, in the absence of any attempt to run on the narrative, in the stock forms, and in the poetical rather than prosaic word-order of the sentences.
This vignetting can be observed in all lenses.
In this case also the illumination must fall to zero by the vignetting of the pencils coming from objects at the margin of the field of view.
In the case of the dispersive eyepiece, on the contrary, no sharply limited field can arise, but vignetting must occur.
Due to vignetting, this order is approximately but not exactly the same as the order by X-ray flux.