Canon ET-60 Lens Hood - Description:
Canon ET-60 Lens Hood is one of the most important accessories for each lens you own. Canon ET-60 Lens Hood provides multiple functions: it shades the lens from stray light, improving your contrast and image quality; in inclement weather. Canon ET-60 Lens Hood can assist in keeping moisture or wind-blown debris off the lens; and it protects the front barrel from the inevitable impacts against walls, door frames, and other real-life obstacles. Almost all EF and TS-E lenses have a Canon lens hood engineered specifically for it.
Canon ET-60 Lens Hood is Compatible with the CANON EF 75-300mm f/4.0-5.6 USM, II, II USM, III & III USM Lenses.

The Canon ET-60 Lens Hood fits the affordable Canon 300mm lens but if you're using Canon ET-60 Lens Hood with, for example, a Rebel 300D or XT, it will also fit onto the standard 18-55mm lens -- however, when fully zoomed out, part of the Canon ET-60 Lens Hood is visible, creating somewhat of a circle in the frame. Canon ET-60 Lens Hood looks really cool, gives it a fisheye sort of feel. In regards to the 300 use, Canon ET-60 Lens Hood seems to work pretty well in bright sun or late afternoon. As most people probably have said, lens hoods in general not only shade the lens from stray light or weird angles of the sun (which often, without a hood, makes the photo hazy or grey) but it also provides protection for the lens itself and filter. It's not much money if you're into photography, and it makes your lens look awesome. If you're a beginner and purchased a 300mm, you don't really need to get the hood. Keep it as something to look forward to once you've got some experience. Either way Canon ET-60 Lens Hood is a nice piece to use.