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Old Sep 3, 2007, 1:31 PM   #1
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shorter lenses seem to have a lens hood that is shaped like this:

and the longer or bigger lenses have this kind:

i know this is a crazy quetion, but it has been bugging me for awhile. thank you, john
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Old Sep 3, 2007, 1:43 PM   #2
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Lens hoods keep stray light from entering into, and bouncing around inside the lens barrel.

Long lenses have a narrower angle of view, so a plain cylindrical lens hood is adequate. But on a wide angle lens, the lens hood looks like this:

You will notice that the cut-outs are positioned at the corners of the exposure.A plain lens hood on a wide angle lens will block some of the angle of view. The cut-outs at the corners of the lens hood are to allow the corners of the exposure to see through the lens hood to the scenery beyond, while still blocking off-angle light from entering the lens barrel.
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Old Sep 3, 2007, 6:29 PM   #3
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TCav is right and the longest real lens that I know of that has a 'petal' type lens hood is the Sigma 100-300mm although the 50-500mm also uses one but I don't class that as a real example as the lens extends during zooming.

You will also notice that wider lenses where the lens rotates when zooming or focusing that it they have to have a normal hood.
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