The Samyang lens hood is for the 800mm f8 MC IF Mirror lens.
The Lens hoods protect and shades the lens against direct sun, incidental light and light reflections from water, snow and other surfaces.reducing halation, lens flares, ghosting, internal reflections and general degradation of the image caused by unwanted light sources.
Lens hoods improve the contrast on a photograph, and also functions as some protection against damage to the front lens element.
The hood is mounted with the use of the filter thread and is made of high quality metal. Internally the hood has been properly blackened and crimped, which prevents internal reflections.