A range finder for a cap for determining the distance to a golf flag. The range finder has a cap coupling portion having a thin shell portion adapted to conform with the cap and a pair of "u" shaped portions for hooking around an edge of the cap. A base is carried by the cap coupling portion. A first support is pivotally mounted to the base at a first pivot point. A lens is carried by the first support. A second support is pivotally mounted to the base at a second pivot point. An index for viewing through the lens is pivotally carried by the second support. The range finder has a linkage bar pivotally mounted at a third pivot point to the first support and pivotally mounted at a four pivot point to the second support. Moving the lens from a retracted position to a flipped down, in use position moves the index in unison.