[KenCo]

I have added a review of this lens but it was sugested I post here also so you lot could discuss it if you'd like to.
Please bear in mind though I have little knowledge of lenses in general and these are just my thoughts on why I chose the 17-55 over the 17-40......

If all your photography is going to be on bright sunny, high contrast days or you only shoot landscapes and always carry a tripod then you probably won’t need a lens like this. However, if you find you may ALSO be shooting indoors or low light and or you just want available light without flash AND don’t want the hassle of carrying or changing other lenses and tripod, then this lens really comes into its own. Indeed if you are looking for a mid range zoom lens for your crop sensor body, with a constant aperture throughout the focal range, whilst also benefiting from image stabilization and including an ultra sonic motor…..then this is the only lens on the market! A complete mid range all rounder!!!
The lens does extend on zoom but does not rotate even when focussing, it also features FTM allowing manual focus when in auto focus mode also the twist zoom action is fairly smooth, damped and does not creep. Its (L series) optics are let down slightly by its build quality and to some by the lack of a red ring, it’s also disappointing that a lens hood (and fancy case) are not included in the price.
I have no problems shooting at F2.8 with this lens at all focal lengths, it has nice contrast and colour rendition coupled with a creamy blur bokeh. Without Image Stabilization this would still be a top lens BUT with Image Stabilization it dramatically expands photographic opportunities and sets it apart from other lenses in this range. The IS system is also compatible when tripod mounted alleviating the need to switch it off, reducing mirror slap, shutter and tripod vibrations…..I haven’t yet done any seriously lengthy exposures but have not had any problems with the many 30 sec exposures I have shot.
There are downsides to EVERY lens and this is no exception.
Build quality, weather sealing, Barrel distortion, pin cushion, chromatic aberration, light fall off and flare are better, worse or completely non existent (in the case of weather sealing) compared to some L lenses and with the exception of build quality and weather sealing, all can be corrected in Photoshop…..Having said that, I have only ever corrected lens distortion.

I pondered for sometime between the 17-55 & 17-40, the 17-55 costs more (but you will always pay more for F2.8 constant aperture, usm and certainly stabilization), it isn’t weather sealed and build quality isn’t as good……BUT the 17-55’s Sharpness is reportedly better, though it’s the versatility that swung it for me. It’s excellent for landscapes and equally so in those low light conditions with an f2.8 constant aperture, add an extra 15mm on the long end and to top it off image stabilization. I have only one L lens the 70-200 f2.8 is usm and to me the image quality from the 17-55 is up there with it….needles to say I sold my kit lens (18-55) and 50mm F1.8.
These comments are just my opinion and truthfully I have no real experience of L lenses in this focal range but, I’d certainly recommend this lens to anyone who may find themselves shooting in conditions previously described….If you can, go to a shop and try it, you will be pleasantly surprised with what this lens can achieve.

Ken.