“Bottom line, the Canon 24-105mm f/4 L is a really excellent optic, but one that struggles a bit along the edges and in the corners with full-frame bodies. As such, it’s an almost ideal candidate for use with DxO Optics Pro, particularly if you’re shooting with a full-frame dSLR.”
Translation: “This lens sucks for its intended market.”
A translation of the translation
For APS-C dSLRs: Compare this to the 18-200mm f/3.5-5.6G VR which is better in every way and cost me $650. Okay, perhaps there is a range around 80-110mm where the Canon lens is f/4 and the Nikon is f/4.5 and the build quality on the zoom ring leaves a little to be desired. Basically on an APS-C body (Canon 300D, 350D, 10D, 20D, 30D) you are paying $1300 for a kit lens and the ignominy of purchasing an “L” lens that screams rip-off. Canon photogs would be better served by the EF-S 17-85MM f4-5.6 IS USM at a slightly overpriced $580—I say this because the 17-85mm lacks a UD element and skimps on the aspherics.
For “full frame” dSLRs: Whenever you hear someone say a lens is “an almost ideal candidate for use with DxO Optics Pro”, you should read this as, “this lens sucks for digital.” DxO is designed to compensate, not fix problems with your optics and digital sensor. If you have vignetting, you can compensate by digitally gaining the picture near the edges, but if contrast on the corners is bad, that means that sharpness is bad because contrast and sharpness are synonymous! When you digitally gain the picture, you digitally gain the noise and add posterization. You can make a similar argument about chromatic aberration. Not exactly someone you want in a mid-level $1300 lens. (I can’t emphasize the price enough because it boggles the mind that anyone but Canon would be so shameless to charge $1300 for this pile of crap.)
So when isn’t this a pile of crap? On 35mm film bodies. I realize this is a late model lens, but it was so obviously designed for a 35mm film body—the trifecta of severe lateral CA, corner softness, and vignetting are a dead give away. All of those imply a very strong angle of incidence near the corners instead of a telecentric one. 35mm film is immune to the angle of incidence, but digital sensors are not. Canon designed this for 35mm film and then marketed this lens toward APS-C digital users who like being ripped off $700 so they can own a “baby L” with a constant (but dim) aperture.
Read between the lines of all the glowing reviews and you see a remarkable consistency among them. Sure, you can follow their advice and buy this this if you need a kit lens now for your 30D and dream of “going full frame” later, but I recommend you buy something cheaper and put the $600-$1100 you just saved into a bank for buying a 5D.
Just my opinions and I’m sure there are a lot of 24-105mm f/4L owners who disagree.