Lens hoods are one of those equipment items that everyone has seen, but still cause a certain amount of confusion among new photographers. Here is a brief rundown of what lens hoods are designed for, when (and how) you should use them.
What They Do
Lens hoods reduce flare, and prevent stray light from entering the field of vision on your lens. While lens flares can often be a fun element of a photo, they can also become highly distracting, so if you want to reduce and eliminate lens flare, use a lens hood.
Types of Lens Hoods
Hoods typically come in either cylindrical, or the slightly more complex petal design. The cylindrical hood will generally work well and get the job done, however, the petal design hoods are also quite popular, is the longer edges of the hood will completely block stray light, while the shorter edges will let more light into the lens than with a cylindrical hood shape.
How To Use Them
Generally speaking, lens hoods work best on lenses that are not considered wide angle. If you put a lens hood on a wide angle lens, you run the risk of the lens hood actually appearing in your image, creating a heavy (and solid black!) vignette. Hoods work best on normal, telephoto and zoom lenses.
When To Use Them
Any time your subject is backlit, or you are shooting into/near the sun, you are bound to get a lens flare, so this is the perfect time for a lens hood. Also, if you are using an off-camera flash (or just about any bright, off-camera light source) you may find that your light source is generating a lens flare. Therefore, indoor, flash photography often requires a lens hood.