zoom lock

besides the new 24-70 f2.8L USM, are there other Canon zooms with this?

my 17-55 f2.8 IS USM didnt have one. obviously there was zoom creep as it got loosened up but i dont see any need for this..

is there an underlying reason for creating and implementing this?

I rented a 100-400 and you twisted the a ring to adjust the tension on the zoom. If you twisted enough it would prevent the barrel from moving. rick

The 70-300 DO IS also has it. It's there because these lenses can extend under their own weight (if you point it downwards, obviously!). I normally only lock them when I've finished shooting - otherwise it gets annoying having to unlock it all the time - you go for a quick shot, try to zoom and find that it's locked!

Steve

The EFS 18-200 has a zoom lock at 18 to prevent zoom creep.

The Tamron 17-50mm does too.

The 70-300 IS USM also has it, but I haven't needed it yet (no zoom creep).