FIG. 1 is a right front, perspective view of a magnifier; FIG. 2 is a front elevational view thereof; FIG. 3 is a rear elevational view thereof; FIG. 4 is a right side view thereof; FIG. 5 is a left side view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof. The broken lines in the drawings depict portions of the magnifier and form no part of the claimed design.