What is the function of a lens hood?

Question

I've tried taking shots with and without it, but I can't see any difference...

Answer 1

You may not see much difference under many shooting conditions. Oddly enough, I made a demo of the extreme just a couple of days ago and your question prompted me to upload it now. Bear in mind that this was shot to create as much flare as I possibly could, so it's not exactly a normal shot. See: http://www.flickr.com/photos/samfeinstein/1478663087/

Here are two images made within less than 30 seconds of each other – one with the lens hood and one without. This is admittedly an extreme example as I was all but shooting directly into the sun to cause this flare and general washout for demonstration purposes.
You will note that the bottom photo is still rather washed out, because of the strong influence of the sun, but it is a great improvement over the top image that is almost completely washed out by lens flare.
The only difference between the two images is the use of the lens hood on one and not on the other. There was a very slight difference in the auto-exposure settings because there was more light in the un-hooded shot.

Answer 2

The purpose of a lens hood is to prevent flare, which can seriously degrade the image quality of photographic lenses. A longer hood offers better flare protection than a short hood, but when the hood exceeds a critical length vignetting sets in. Therefore, a lens hood needs to be carefully chosen. The optimum hood depends on the philosophy behind the hood, with the shape and size as the key parameters, and on the lens aperture and subject matter. Several lens hood considerations will pass in review in this article. I will not discuss issues such as choice of material - I leave it to the imagination of the reader that an effectively blackened hood is more useful than one whose interior shines as a mirror. Rather, I concentrate on size and shapes. Although I am the first to admit that the contents are partly of an academic nature, the material could be vital for those readers who strive after the best possible image quality. THE DIFFERENCE MAY NOT BE SO NOTICEABLE...: ) I HOPE I WAS HELPFUL

Answer 3

Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended you also get the added benefit of some extra protection from accidental impact.

This plastic snap-on lens hood is designed for wide angle lenses with a focal lenght as wide as 24mm. Includes plastic hood cap.

Note: Not for lenses where the filter threads rotate, such as some zoom lenses.

Answer 4

Imagine playing center field wearing a beanie, instead of a baseball cap with a brim. During night games, or when it's overcast, you wouldn't notice the difference (though you'd look awfully silly).

But, when the sun is shining on your face and the ball is in that bright sky, you'd be wishing you had something to cut the harsh glare. You might use a hand to shade yourself, but a cap's brim would be priceless.

A lens hood, for me, is a must. I've had too many photos ruined because lights and reflections crept onto the front element of my lens and washed out the picture.

Answer 5

As already stated a lens hood helps prevent image degradation from stray light sources.

They also offer some protection from accidental bumps that lenses sometimes suffer.

However, lens hoods are not generic - each lens has its own dedicated lens hood. A lens hood for a 50mm lens would cause vignetting (darkening of the corners) on a 35mm or 28mm or 24mm lens. A lens hood for a 300mm lens would cause vignetting on a 100mm lens.

Answer 6

There are also petal-shaped lens hoods which help prevent the lens hood from obscuring the light from a built-in flash. There is also the thought that they can help prevent artifacts (unwanted spots) in digital images. No lens hood will totally prevent lens flare when shooting into direct sunlight or other light source.

Answer 7

Lens hoods are used to prevent flare. They come in especially helpful when your shooting outdoors in bright sunlight.

hope this helps