Think Tank Hydrophobia 300-600 V2.0 Rain Cover for 300 f/2.8 Up to 600 f/4 Lens Hydrophobia 300-600 V2.0 protects the camera and allows full operational use when the rain cover is deployed The Hydrophobia 300-600 V2.0 pre-mounts to the lens hood to be quickly deployed during inclement weather. If bad weather is intermittent, the rain cover can stay in the pre-mounted position but pulled out to cover the camera when needed The rain cover can be attached while the DSLR is attached to the lens. To deploy from the pre-mounted position, loosen the red elastic cord at the bottom, then simply pull the rain cover fabric out from underneath the flap A clear flap is designed to cover the Hydrophobia eyepiece while the camera is not in use. The flap prevents any droplets from falling into the viewfinder and obscuring vision when ready to shoot Hydrophobia 300-600 V2.0 now offers a larger clear window on back for increased view of the camera and LCD screen