A slip-on shutter works well with larger, heavier lenses like Petzvals, which have a straight hood. It consists of a close-fitting leather collar which slips over the hood, to which the lightweight shutter guide is attached (as above) . The shutter blade fits into the guide, covering the lens until it’s released. The beauty of the slip-on shutter is that the lens is completely uncovered right up until the point where you slip it on to take the shot, so everyone can admire it’s glorious brassiness. It takes seconds to fit, and can be removed again as soon as you’ve taken the photo (and covered the film with the dark slide!). Another benefit is that is doesn’t interfere with the lens mount in any way, and shutter blades are very unlikely to get caught up in other parts of the camera or tripod.