Accessories for camera lenses run the gamut from things that protect your camera gear to gadgets that enhance what the lenses do. It's always a good idea to buy a couple of spare lens covers, as they can easily get lost as you put them on and take them off, but there are other lens accessories that are also well worth considering.
Lens shades increase picture quality by cutting out extraneous light, which can do nasty things to your pictures. Some lenses come with a shade. If yours didn't and you want to use one, you'll need to buy one that fits each lens, both in terms of the filter size of the lens (the diameter of the threaded front of the lens) and the focal length.
A wide-angle lens can only handle a shallow shade. If you put a telephoto shade on a wide-angle lens or wide-angle zoom lens, you are likely to experience vignetting, or a darkening of the corners of your picture. You won't see it through the lens, but you'll definitely see it on your prints.
Lens filters change the way in which light reaches the film. In so doing, they also change the way in which images will appear on film. Some filters simply enhance things, such as making colors look more true or eliminating glare and reflections from shiny surfaces. Other filters are used to create special effects such as softening the focus on portraits.
The one filter that's a must-have is an ultraviolet or UV filter. Also known as haze filters, they cut down the ultraviolet light, or visual haze, that you can't see but your camera can. Even more important, they protect the delicate lens of your camera from dust and other elements that can harm it. They're relatively cheap, so buy one to fit every camera lens you own, and keep it on the lens unless you're using another filter.
Other filter types to consider adding to your gear bag include the following:
Polarizing. Just like sunglasses with Polaroid lenses, these filters cancel reflections and glare caused by shiny surfaces and enhance blue skies on color film. The best ones rotate 360° in their mounts to control how much they cancel reflections or darken the sky.
Star filters. These specialized filters have grids etched into them that turn light into stars. There are several different types available; the best allow you to rotate the grids to control how many points the stars have, as well as their direction.
Light balancing. These filters reduce the amount of light coming through the lens or balance the color of artificial light.
There are literally dozens of different types of filters. The categories of lenses listed above cover only your primary needs.
Also known as teleconverters or extension rings, these tube-like devices increase the focal length of a lens and make it capable of greater magnification. Although the images they render aren't as sharp as those made with a true telephoto lens, they're a cheap alternative, especially if you don't plan to use one very often. Tele-extenders also require you to focus manually in most cases.