Quote:
Originally Posted by klara
Whats a lens hood?
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A lens hood attaches to the front of the lens. They look like black bowls without a bottom.
A lens hood serves three purposes:
1) prevents non-image forming light from entering the camera
2) prevents direct light from sources such as the sun from striking the front of the lens
3) provides physical protection to both the filter threads and the front lens element
OK, before you ask...
What is non-image forming light? Camera lenses admit light into the camera beyond the size of the film or image sensor. If that light is not controlled, the result is body flare and loss of contrast. The inside of the camera is flocked with flat black paint and/or black fuzzy stuff to minimize the effects of non-image forming light, but a properly designed and sized lens hood will prevent it from getting inside in the first place.
Direct light striking the front of the lens can and will lower image contrast, and in the case of lenses with poor coating, flare and ghost like crazy. A proper hood will eliminate this. There is a "but" though... Wide angle lenses, because of their angle of view, are difficult to hood for flare. That's why you see some hoods that are "tulip" shaped, they maximize the "hood to angle of view" ratio.
As far as physical protection... I like metal hoods because thay WILL protect the front of the lens MUCH better than a rubber hood (rubber gives, metal fights back). On long lenses, a stout metal hood will draw blood before it gives way! (the hood on my 300mm f/4.5 EDIF Nikkor has proof on it, as does the hood for my 80-200 f/2.8) :-)