The field of the present invention generally relates to devices for actuating an adjustable feature on a sighting device such as a riflescope or spotting scope or other types of telescopic optical systems.
Telescopic sighting devices such as riflescopes, binoculars and telescopes may include an external adjustment mechanism or knob for actuating an inner working of the scope. For example, a riflescope is commonly used by hunters to aim their rifle at selected targets. Because bullet trajectory, wind conditions, and distance to the target can vary depending upon shooting conditions, quality riflescopes typically provide compensation for variations in these conditions by allowing a shooter to make small adjustments to the optical characteristics or the aiming of the riflescope relative to the firearm on which it is mounted. These adjustments are known as elevation and windage adjustments, and are typically accomplished by lateral movement of an adjusting member, such as a reticle located within the riflescope, as shown in U.S. Pat. No. 3,058,391 of Leupold, or pivotal movement of lenses mounted to a pivot tube within a housing of the riflescope to divert the optical path of the observed light before it reaches the reticle, as shown in U.S. Pat. Nos. 3,297,389 and 4,408,842 of Gibson. In these designs, a shooter accomplishes adjustment of windage and holdover by way of two laterally protruding adjustment knobs or adjustment screws, typically extended at right angles to each other, that are operatively connected to the adjusting member. A spring located between the housing and the adjusting member opposite the adjustment knobs biases the adjusting member against the adjustment knobs so that the adjusting member follows the movement of plunger screws of the adjustment knobs. Another external adjustment mechanism is focus. U.S. Pat. No. 6,351,907 discloses an external focus adjustment mechanism by which the position of an internal lens element is axially adjusted to change focus.
In these various external adjustment mechanisms, the adjustment knobs may be sealed to the housing to maintain a dry or inert gas charge within the interior of the housing to prevent fogging and condensation on internal lens surfaces.
It is desirable for these adjustment mechanisms or knobs to be readily accessible, and yet include some means to inhibit the adjustment from being inadvertently adjusted, such as bumping against the knob. One way of preventing such inadvertent adjustment is by providing a removable cap. The cap provides both physical protection from fouling or damage as well as physical isolation from inadvertent adjustment, but the cap must be removed in order to access the internal adjustment mechanism. Moreover, once the cap is removed, the user typically places it in a pocket or other location whereby the cap may be lost.