I claim the ornamental design for field glasses, as shown and described.
FIG. 1 is a top perspective view of the field glasses;
FIG. 2 is a bottom perspective view of the field glasses shown in FIG. 1;
FIG. 3 is a top plan view of the field glasses;
FIG. 4 is another top perspective view of the field glasses;
FIG. 5 is another top perspective view of the field glasses; and,
FIG. 6 is another top perspective view of the field glasses.
The broken lines shown represent unclaimed subject matter and form no part of the claimed design. The shade lines shown represent surface shading and not surface ornamentation, color, or material type.