Why 'Petal' lens hoods?

Can anyone tell me if there is any scientific or optical reason why most of the lens hoods for the upmarket lenses seem to be what is called 'petal shaped'? I can't seem to see any sense in it (although I'm sure one of you boffins will put me right).

It would seem to me, without any science to back it up, that the most sensible shape for a lens hood would be rectangular. This surely would mimic the shape of the sensor and be a more effective shield. I once owned a Hasselblad and I remember that that had a square lens hood (again, mimicing the film format), so it is not a new idea.

The 'petal' hoods are used on wider angle lenses (17-40, 16-35, heck even the 24-70 exhibits a petal detent) these are shaped perfectly so that when the lens is at it's widest setting the hood does not appear in the photos, yet still are shaped so that flare and glare can be controlled.

Thank You, I was wondering myself. Hood on my Tamron 17-50 F/2.8

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Actually there is no reason that the entire lens couldn't be made rectangular, except that it is much easier to design and manufacture circular lenses. After that, the shape of the lens hood is probably a combination of esthetics, manufacturing ease and marketing.

The petal shape allows a longer hood on the top and bottom, an medium hood on the sides and a shorter hood on the corners. A rectangular hood could not have the corners any longer than the corner portion of a circular hood. The top, bottom and sides could still stick out further resulting in petals on a rectangle. The problem with this is that the petals would be flat and more subject to deformation or damage than the petals on a circular hood.

Don't know about the hood, but I like that lens cap design.

This one.

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I love that lens cap design too - why on earth don't Canon do it? It would save an awful lot of fiddling around!

ScottE wrote in post #2614825
Actually there is no reason that the entire lens couldn't be made rectangular, except that it is much easier to design and manufacture circular lenses. After that, the shape of the lens hood is probably a combination of esthetics, manufacturing ease and marketing.

I can think of several reasons, not the least of which is focusing and zooming.

20drgoger - would you care to elaborate?

does the petal hood have to be alwayz sitting in the same way?
or can you just screw it in and it doesnt matter where the petals sit above the lens?

verty wrote in post #2615509
does the petal hood have to be alwayz sitting in the same way?
or can you just screw it in and it doesnt matter where the petals sit above the lens?

Circular hoods (like the 50/1.4's hood) sometimes have threading that allows the hood to settle in various positions. Petal ones only lock into the correct position (long edge top and bottom).

Roy Mathers wrote in post #2615486
20drgoger - would you care to elaborate?

Many lenses are designed so that the elements rotate when focusing or zooming which would not be possible if the lens elements were rectangular. However, it is possible to design a lens where the elements move without rotating.

linarms wrote in post #2615528
Circular hoods (like the 50/1.4's hood) sometimes have threading that allows the hood to settle in various positions. Petal ones only lock into the correct position (long edge top and bottom).

thanx for that! ive always wondered if that was the case

verty wrote in post #2615509
does the petal hood have to be alwayz sitting in the same way?
or can you just screw it in and it doesnt matter where the petals sit above the lens?

you can try locking the hood on, and then turning it back slightly. depending on the lens the and crop factor of the camea, you'll notice immediately why hood are petal-shaped. and unless they're in the correct position, they'll show up in the image.

calgaryphotographer wrote in post #2614771
The 'petal' hoods are used on wider angle lenses (17-40, 16-35, heck even the 24-70 exhibits a petal detent) these are shaped perfectly so that when the lens is at it's widest setting the hood does not appear in the photos, yet still are shaped so that flare and glare can be controlled.

even certain tele's have petal-shaped hoods. i know my 70-200/2.8 IS does.