A rifle scope has a body with a number of optical elements. An adjustment knob is rotated we connected to the body and interacts with at least one of the optical elements to provide an image shift in response to rotation of the knob. A detent mechanism interacts with the knob, and has a number of detent positions. Many of the detent positions have a first detent force, and a selected subset the detent positions have a greater second force. The selected subset of detent positions may correspond to selected major distance intervals.