Abstract: A rotation assist assembly is an assembly for assisting the rotation of a rotary adjustment member included in a lens barrel, and includes a base portion and a grip portion. The base portion is configured to be wound around the rotary adjustment member along a rotation direction of the rotary adjustment member. The grip portion is coupled to the base portion in the rotation direction, and a user's finger is placed on this grip portion when rotating the rotary adjustment member. A first maximum dimension from a rotational center of the rotary adjustment member to an outer face of the grip portion in a radial direction of the rotary adjustment member is greater than a second maximum dimension from the rotational center to a radial outer face of the base portion.