The Olympus hoods for their rangefinders are cylindrical so they do not interfere with the viewfinder. They clamp onto the outside ot the lens to provide the extra diameter to not cut off any of the image. This also leaves the filter ring free for filters. I have always found lens hoods of any type to be a pain, and prefer to wear a ball cap. This can be used to shade the camera at times when the sun might be a problem