A veriable speed unit includes base, a first sliding component, a second sliding component and retaining device in which the base has a first surface, the first sliding component being able to slide on the first surface has a second surface with the second component sliding on it having a third surface contacting with a drive component for driving an optical element. The retaining device fixes the first sliding component on the base or the second sliding component when which is pushed, the first sliding component will be fixed on the base or on the second sliding component to provide different moving speeds to the driven units to drive optical elements. |