The ornamental design for a lensbarrel for a telescope, as shown and described.
FIG. 1 is a front, top, and left side perspective view of a lens barrel for a telescope showing my new design;
FIG. 2 is a rear, bottom, and right side perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a right side view thereof; and,
FIG. 8 is a left side view thereof.
The features shown in broken lines in the drawings depict environmental subject matter only and form no part of the claimed design. The dash-dotted lines denote the boundary of the claim and form no part of the claimed design.