One of the most key pieces of equipment that I use is a lens hood. You would be amazed at the difference that one makes in your images. If you purchase a brand name lens that is the same as your camera, you probably won’t have one included with your lens and have to pay more to get one. But, is that really the lens shade you should be using? Is it even worth the added space in your camera bag to have a lens hood?
A lens hood is used to block the light coming in from the side of the lens, and prevent flare. Key to choosing a lens hood is making sure you get one long enough to prevent flare and shade the lens, but not so long that you end up with a vignette. This means your focal length on a lens impacts your lens shade. If you have a zoom lens, the shade is often designed for the smallest focal length and not the longer lengths.
Lens flare is many things. It mostly shows up at bright spots the shape of the aperture on your images (aperture ghosting), but could be a lack of contrast in the image (veiling glare) or where it looks like a bright haze is washing off a side of the image (filter flare or partial veiling glare). It could even be a ghost. Flare occurs because light hits the sensor or film at the wrong angle from what it is intended. They form from light entering the lens at too steep an angle, refraction at the joints of two pieces of glass in a lens, and even reflections from the glass within the lens itself (or attached filters or the film/sensor itself). Anti-glare coatings help a lot, but aren’t a total solution. Making sure you keep your front lens clean and free of chips will also help a lot. The best solution is to always have a lens hood on your lens, too.
A vignette is a fading of the image into the surrounding, usually black or white in color. In this situation, we are talking about when this happens unintentionally and is always dark. Vignetting is most noticeable in the corners of an image – more so with shorter lens focal lengths. It can be caused by using a lens hood that is designed for a longer focal length lens, when too many filters are attached to the lens (one can be too much for an extreme wide angle lens), when you use too many extension tubes or bellows (illumination falloff), or problems in the design of the lens that when you open it up there is a hot spot in the center of the image but goes away when stopped down to F4 or so (optical vignetting).
After several tests, one thing has become very apparent: one lens shade doesn’t fit all lenses with their use. I frequently use primes and full frame lenses. The shades are designed to be used with full frame sensors – but I also use them with smaller sensors, too. This makes the shade less effective with the smaller sensors as the shade won’t cover the correct area. When I started photography, there were expensive bellows lens shades that we used in the studio and either full metal or inexpensive round plastic lens shades for outside. Today, most lenses have inexpensive plastic lens shades in a tulip shape and use a bayonet mount. The tulip shape was originally designed to give better long focal length performance without sacrificing shorter focal length performance. In reality, they do well at short lengths but aren’t much good at longer lengths.
My $0.02 is that if you buy a good lens, you should also have a lens hood as standard equipment. Even if the lens hood isn’t the best one for the lens, something should be used. If you have the money to spend on an adjustable bellows type hood, then do it. You will never buy another in your life if you don’t abuse it. You couldn’t be more wrong by saying that your lens is so good you don’t need a lens hood. The lens hood also doubles as extra protection from harm to your front lens element, too. Don’t undervalue this key piece of equipment. Next on shading the lens will be the use of flags.
Edit: There is also optical vignetting that occurs when the subject is usually a light source or reflection and darkens around the subject. An easy to give example is taking Christmas lights (or similar type of lights) and shooting them out of focus. For those of you who use large format cameras or tilt-shift lenses, you also have off access vignetting from tilting a lens so far that the light cone shows on your film plane.