A pictorial device Beato often used in his photographs of people is the vignette, which highlights the subject with an oval window that fades to white toward the edges of the image. Beato made a vignette by placing a template with an oval opening on top of the glass negative during contact printing.
Why did Beato use the vignette? Was he covering up the falling off of the image at the edges caused by the lens he used, or by his use of an open aperture, with the resulting shallow depth-of-field (the background is out of focus), which enabled him to have a shorter exposure time? Also, vignettes were fairly common at the time in portrait photography, perhaps mimicking the oval frame sometimes used in painted portraits.
Whatever the reason, the vignette creates a peephole through which we spy on this fascinating array of people in feudal Japan.