Sight adjusting mechanism

A sight adjusting mechanism, comprising:

• an adjusting knob, having a penetrating hole;
• an adjusting ring member, having a first through hole, wherein the adjusting knob couples with the adjusting ring member by means of a fixing fastener;
• a base, having a second through hole;
• an adjusting bolt, comprising an upper-side portion and a lower-side portion, wherein the upper-side portion of the adjusting bolt enters the first through hole of the adjusting ring member to couple with the adjusting ring member and the lower-side portion of the adjusting bolt enters the second through hole of the base to couple with the base such that the adjusting bolt can only move along an axis during the adjusting knob rotates;
• a limiting member, disposed in the penetrating hole of the adjusting knob;
• and
• a positioning ring, mounted on the adjusting ring member,
• wherein the limiting member is operable at a first position and a second position along the direction of the axis, the limiting member connects with the positioning ring and the adjusting knob is restricted to rotate within a range of predetermined angle when the limiting member is located at the first position, and the limiting member departs from the positioning ring and the adjusting knob rotates in an angular range that is greater than the predetermined angle when the limiting member is located at the second position.