what are these, and where do i buy them?

[youyesyou.net]

what is the thing on the tip of the lense called and what is their purpose?

http://www.zone-numerique.com/uploads/Appareils/Sigma/18-125-DC/18-125-34-paresoleil-300.jpg

http://www.digitalsecrets.net/secrets/Photos_4_web/CanonDR+SigmaMed.jpg

[Harry Settle]

Lens hoods. They are supposed to decrease the amount of direct light that might hit the lens glass causing flare.

[ScottE]

They also provide mechanical protection to the front of the lens. If your camera and lens happens to swing into something it is better to have it knock the lens hood than the front element of the lens that can be scratched or the rim that the filter screws into that can be bent.

I never carry my camera around without a hood on the lens.

Most lens manufacturers supply them with their lenses. Canon supplies them with L lenses, but for some reason does not supply them with the non-L glass.

Scott

[youyesyou.net]

can i buy the "hoods" for other cannon eos lenses? and where can i buy them? ritzcamera.com, ebay.com?

[lostdoggy]

What lens do you plan to put it on. If you plan to put it on the kit lens forget it.The kit lens is a has a front focusing mechanism that turns when it focus and the petal hood you posted will only work on wideangle lenses that does not turn during focusing. Wideangle lens needs the shorter sides to accomadate the extra width of view.

[tim]

You can buy hoods for any lens, just be careful to get the right one.

[Curtis N]

what is the thing on the tip of the lense called and what is their purpose?Compensation factor.
They make the lens look bigger than it really is, and also makes it look more expensive, which results in more people looking at it and saying, "wow! cool camera!" So it's a sort of a combination ego boost/babe magnet.

That, and what the other guys said.

[boomer1959]

Lens hood, an absolute must on any lens. :D

[jfrancho]

What lens do you plan to put it on. If you plan to put it on the kit lens forget it.The kit lens is a has a front focusing mechanism that turns when it focus and the petal hood you posted will only work on wideangle lenses that does not turn during focusing. Wideangle lens needs the shorter sides to accomadate the extra width of view.That doesn't mean it can't have a hood. Canon makes a hood for the kit lens, see here (http://www.bhphotovideo.com/bnh/controller/home?O=cart&A=details&Q=&sku=70568&is=REG&addedTroughValue=351554_USA&addedTroughType=accessory).

[EOSAddict]

Even if I don't use it as a hood, I always fit it wrong way round to protect the lens. When I dropped my previous Sigma 75-300 the lens hood took all the impact and the lens was saved!