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Old Mar 1, 2008, 9:52 AM   #1
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Why petal lens hoods? Why do some lenses come with them and other "cylindrical"? It seems most lenses come with petal versus cylindrical. Do the petal do better jobs of lessening glare?
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Old Mar 1, 2008, 10:25 AM   #2
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I think the easiest answer is to state that the petal shape provides the best "performance" for the shading for taking rectangular photos, most of which have a rough aspect ratio of 3:2 (hence the long and short petals). Additionally, the petal shape minimizes vignetting. Obviously, you must be sure that the longer petals are at the top and bottom of the lens, with the shorter to the left and right, due to that rectangular 3:2 aspect ratio.

Lenses that use cylindrical lenshoods are long enough that they don't "see" the hood and therefore do not vignette. Additionally, rounded lens hoods are a must for lenses where the end rotates when you zoom or focus.

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Old Mar 1, 2008, 10:25 AM   #3
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I think it has to do with the focal length of the lens, not particularly with reducing glare although the petal lengths would be maximized for the FL. Wide lenses need the petal shape so the hood doesn't interfere with the frame. Anythingbelow around 50mm EFL will probably have a petal shaped hood.
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Old Mar 1, 2008, 10:26 AM   #4
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DarkDTSHD wrote:
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Do the petal do better jobs of lessening glare?
No. They do a better job of lessening vignetting.

Lens hoods block off-axis light that would bounce around inside the lens barrel. A cylindrical lens hood is equally effective at blocking light from any direction. A petal lens hood blocks more light from the top, bottom, left and right, without obscuring objects within view at the corners.

Unfortunately, on superzooms, a petal lens hood has to accomodate the widest angle of view, which means that it isn't very effective at the narrowest angle of view.
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Old Mar 1, 2008, 10:56 AM   #5
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Ok thanks people. The petal hood on my 28-70 is HUGE!!
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Old Mar 1, 2008, 5:56 PM   #6
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DarkDTSHD wrote:
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Ok thanks people. The petal hood on my 28-70 is HUGE!!
Yeap, but that was designed for a full-frame...
-> Most of the hood would go to waste since your 1.5x crop camera have a much narrower FOV
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Old Mar 1, 2008, 6:18 PM   #7
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NHL wrote:
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DarkDTSHD wrote:
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Ok thanks people. The petal hood on my 28-70 is HUGE!!
Yeap, but that was designed for a full-frame...
-> Most of the hood would go to waste since your 1.5x crop camera have a much narrower FOV
I thought I'd prepare myself for when Nikon puts out a FX boxy based on the D300 body.

Onto other topics...
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