A lens hood The most important accessory that you can purchase is a lens hood. Some manufacturers include a lens hood with the lens, but most do not. The hood is simply a metal, plastic or rubber shade that attaches to the front of the lens. Its function is to shade the front surface of the lens from flare-producing light. Flare can drastically lower contrast and in severe cases produce the characteristic multicolored circles that were so popular in spaghetti westerns.
Hoods also offer some protection against bumps and knocks.
If possible, purchase the hood made specifically for a lens. The filters don't have much visible effect on the photographs but will protect the vulnerable front elements of lenses from scratches, liquids and dirt. The ultraviolet or skylight filters will perform virtually identically, although the skylight filter will add a bit of warmth to slide film. It is much cheaper to replace a scratched filter than to replace a scratched front lens element. No matter how steady your hands, even slight trembles become apparent on film.