Certain embodiments described herein comprise a scope for mounting on a firearm to provide a sight. This scope is adjustable in at least one of elevation and windage. The scope comprises a main tube, imaging optics in the main tube, a movable optic assembly that holds at least a portion of the optics; and an adjustable mechanism configured to adjust the position of the movable optics assembly. The adjustment mechanism comprises a rotatable adjustment knob, an adjustment screw, and a biasing element that biases the adjustment screw with respect to the adjustment knob. In an engagement position the adjustment knob drivingly engages with the adjustment screw such that rotation of the knob causes rotation of the adjustment screw, and in a depressed position the knob disengages the adjustment screw.