I claim the ornamental design for field glasses, as shown and described.
FIG. 1 is an upper perspective view of field glasses showing my new design.
FIG. 2 is another perspective view thereof shown without lens cap covers.
FIG. 3 is a rear perspective view thereof.
FIG. 4 is a lower perspective view thereof.
FIG. 5 is a front view thereof.
FIG. 6 is a rear view thereof.
FIG. 7 is a top view thereof.
FIG. 8 is a bottom view thereof.
FIG. 9 is a left view thereof; and,
FIG. 10 is a right view thereof.
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.