Adjustment mechanisms that may be employed for making operational adjustments to sighting mechanisms such as riflescopes, telescopes, binoculars, monoculars or other types of viewing devices. One configuration being directed to a pop-up cap that is retained and remains connected to the adjustment mechanism, the pop-up cap translating between a first position (typically the closed position) where rotation of the cap does not engage the adjustment mechanism to a second (typically the extended position) where rotation of the cap engages the adjustment mechanism.