Split-Field Diopters allow simultaneous focus on both close-up and faraway subjects. A standard diopter element is precision-cut in half and mounted in the ring.
Frame your subject, focus on the distant background, and move the camera slightly to obtain close focus on the foreground.
Position the slightly out-of-focus line of the cut edge of the glass in an area it won‘t be noticed. Closing the iris will reduce the width of this line.
Without Diopter filter (focus on foreground)
Without Diopter filter (focus on background)
With Split-Field Diopter filter (focus on fore- and background)