Hoodman's HoodEYE Eyecup for Canon 18mm Eyepieces Models will help block out light when looking through your camera's viewfinder. From its oversized design, which seals out ambient light, to its rotating nature that accommodates right- or left-eyed shooters, this eyecup ensures that the Canon 18mm eyepiece shooter can get their shot with ease. The self-locking mount slides over the eyepiece mounting rails, keeping the cup in place. Additionally, the hypoallergenic silicon keeps irritation at bay for hours of comfortable shooting. When used on cameras with articulating screens, the HoodEye Eyecup will prevent full motion, requiring users to remove the eyecup before moving the screen into position.